The following is from the American Edition of Luther’s Lectures on Genesis.
[Genesis 25:]19. These are the descendants of Isaac, Abraham’s son: Abraham was the father of Isaac,
20. and Isaac was forty years old when he took to wife Rebecca, the daughter of Bethuel the Aramean of Paddan-aram, the sister of Laban the Aramean.
I have frequently pointed out—and it must be impressed frequently—that in the accounts of the fathers it is most delightful to see how they are described as true human beings, weak and altogether like us. On the other hand, under that human weakness there were most saintly angels and sons of God. For, what is most surprising, in the kind of life involving the management of a household they had absolutely no unusual or special semblance of saintliness; and when the flesh, that is, the wise men of this world and the monks, sees this weakness, it is greatly offended and has profound contempt for the saintly patriarchs. Thus Augustine confesses about himself that he laughed at the accounts of Isaac and the other patriarchs when he was still a Manichean, because he kept in mind nothing else than that most ordinary kind of life, namely, having a wife, begetting children, having a few sheep and cattle, and living with one’s fellow citizens and neighbors. What could one learn from this that is uncommon or unique? Or why are these seemingly unimportant and unprofitable facts read and presented?
It is indeed a misfortune of the flesh that in this manner it must remain attached to the common weakness in respect to which the fathers are like other people and must therefore be offended and find fault with the ordinary life and invent another, extraordinary kind of life, such as celibacy, monasticism, the priesthood, etc. For an ungodly person must not see the glory of God; he must see only the weak and foolish things and, if I may use this expression, the nullity of God. But he must not see the glory and majesty, the power and wisdom of God, even if they are set before his eyes. Thus here Moses relates in a very simple manner that when Isaac was 40 years old, he married a weak little woman from Mesopotamia in Syria. What is this? Do not other people contract marriages that are similar to this one or sometimes more splendid? Why, then, do we read about these things? I answer that the flesh is permitted to see the human nature and weakness in the saints but by no means to see the divine nature and the saintliness of the angels, in order that it may be offended and seem to have found a reason for inventing new forms of worship in which to put saintliness.
Moreover, it is not without purpose and beside the point when Holy Scripture states that Isaac married Rebecca when he was 40 years old. For it points out that he did not take a wife in the well-known first passion of youth but stood firm for a considerable time in his battle against and victory over the flesh and the devil. For the accounts and the experience of individuals attest how great the impatience of lust is in youth, when the urgent sensation of the flesh begins and the one sex has an ardent desire for the other. This is a malady common to the entire human race, and those who do not resist its first flames and do not suppose that there is something for them to endure, plunge into fornication, adultery, and horrible lusts; or if they take wives rashly and ill-advisedly, they involve themselves in perpetual torture. Accordingly, Isaac endured that conflict and contended most valiantly with the flame and his flesh, because he was a true and complete human being just as we are. Moreover, our nature has been created in such a way that it feels the passions of the flesh at about the twentieth year. To endure and overcome those passions up to the fortieth year is surely a heavy and difficult burden. In this last age our young people refuse to assume this burden; they are unwilling to have patience for a moderate period of time.
Therefore if they take wives during those first manifestations of passion, the devil, who earlier inflamed them with lust, later on cools them down with a breath to the opposite effect and causes them to go to extremes in their hatred of the woman. Those things are truly diabolical. Therefore the heart should first be instructed by the examples of the fathers, in order that it may be able to undertake and keep up that first battle against the flesh. The maturer age, which has arrived at the years of manhood, has its own battles—battles that are greater. During adolescence love begins to learn, just as it is described in adolescents in the works of the comic poets. But the sacred accounts present examples in which the victory, and at the same time the battles against the flesh, are set forth. Thus Isaac, too, felt the flames of lust just as other adolescents do. But he was taught by his father that one must contend against these flames, first by reading Holy Scripture and praying, and then by working, being temperate, and fasting. These should be the exercises of adolescents, at least for one year or two, in order that those who are no longer able to be continent may learn nevertheless what the endurance of lust means. For this, too, is endurance and martyrdom, just as some assume several kinds of martyrdom, among which they count a rich, generous, and chaste young man. Indeed, this man is surely a martyr, because he is crucified every day by the passions of his flesh.
Young people should avoid promiscuity. In order to be able to protect their chastity, they should strengthen their hearts against the raging desire of the flesh by reading and meditating on the psalms and the Word of God. If you feel the flame, take a psalm or one or two chapters of the Bible, and read. When the flame has subsided, then pray. If it is not immediately checked, you should bear it patiently and courageously for one, two, or more years and persist in prayer. But if you can no longer endure and overcome the burning desires of the flesh, ask the Lord to give you a wife with whom you may live in a pleasing manner and in true love. I myself have seen many people who gave free rein to their passions and fell into detestable lusts. But in the end they had to endure woeful punishments; or if on a blind impulse they were fixing their minds on marriage, they got wives who were not at all suited and obedient. This, of course, served them right.
All people should know that they have been called to war against the flesh. This is one battle. The second is against the devil. The third is against the world. Therefore one should not yield immediately to those first impulses, especially in this era, when the hope of marriage has reappeared. We did not have it in the papacy, for he who wanted to become a priest was compelled to vow perpetual celibacy. That papal tyranny has now been brought to light, and true freedom has been restored. Consequently, you should learn to pray and to wage war against the flesh. But then ask God to give you a Rebecca and not a Hagar or someone worse. For a good wife does not come by chance and without God’s guidance; she is a gift and not the result of our own plan or will, as the heathen think.
Isaac was not brought up in this heathen manner. He undoubtedly did not escape the vexation and the flame of his flesh during the 40 years he lived before his marriage, for the flesh contends against the spirit no less in the household than in the government or in the church. But he obeyed his father Abraham, who instructed him to meditate on the commandments of God and by means of sacred studies to arm himself for the first battle. This is why God later on gave him Rebecca, with whom he led a quiet and peaceful life. Holy Scripture points this out in a concealed manner, and in the matter of the weakness that has been mentioned it presents Isaac to us as a most excellent example of a young man’s chastity, which is important because it is a war in which young people are involved. And the chastity of Isaac includes the upbringing and instruction through which he learned to avoid bad company; and evidence is given that he was diligent, meditated, prayed, and engaged in work. Here all this is discernible in a concealed manner in those 40 years during which he lived without a wife.
Moreover, it seems to have been customary at that time for young men not to take wives before they were 40 years old, but for girls to marry when they were 10 years younger, as we saw above in the case of Sarah. I think that Rebecca, too, was 30 years old. After the Flood nearly all the fathers took wives when they were about 30 or 40 years old. Before the Flood they married later; they waited until they were 100, 80, or 90 years of age. After the Flood God accelerated the multiplication of the human race. Therefore the time was shortened, so that men married when they were 40 years old, and the women when they were 30. Consequently, that age was far better and far more excellent than ours. We think that this evil is mitigated by satisfying lust through acts of fornication and adultery, but in this way human beings degenerate altogether into beasts and become unsuited for all good works. If they rush into marriage rashly and without the definite procedure prescribed by God, they do not take wives but incur punishment and perpetual annoyance, because they were without prayer and the fear of God. God forbids this when He says (Ex. 20:7): “You shall not take the name of the Lord your God in vain,” and also (Ps. 50:15): “Call upon Me in the day of trouble.”
“But,” someone will say, “such delaying is very annoying and unbearable.” Right indeed. This is why I stated above that it is on a par with the other exercises in patience by the saints, like the suffering and annoyance of fasting, imprisonment, cold, sicknesses, and tortures. In the same way lust is a serious sickness and burden. But one must resist it and fight against it. Thus later on, when you hold a position in the government, you will be annoyed by other difficulties, such as thefts, robberies, and various kinds of human wickedness. In the church you will have to contend with heretics and with the devil, who assails faith, hope, and the love of God. But you have the Word; you have Holy Scripture, your studies, exercises, and labors. From these your faith will grow and be strengthened. Thus lust, too, when it has been overcome by prayer, will serve to increase faith and prayer. Therefore in these seemingly useless words Holy Scripture presents an outstanding example of Isaac’s chastity and of the very fine discipline that existed in the church and in the house of Abraham.
21. And Isaac prayed to the Lord for his wife, because she was barren; and the Lord granted his prayer, and Rebecca, his wife, conceived.
This is another trial. After the flame of lust has ceased and Isaac has become a husband and has had Rebecca as his wife for 20 years (for so long does God delay the promise in which He had promised his father Abraham: “Through Isaac shall your descendants be named”), another affliction now follows, and indeed one that is far more burdensome than the previous trial. The victor over lust overcame the devil by his chastity up to the time of his marriage. In the marriage state he longs for offspring, in accordance with the promise; and he certainly has no slight hope, since he knows that his wife was prepared for him and brought to him in accordance with God’s plan. But Rebecca does not bear a child; nor does she have a promise that she will be a mother, just as Sarah, too, did not have a promise at first. This undoubtedly troubled his heart, and to this trial were added fear of and worry about perpetual barrenness, which they considered to be a curse. For the fathers laid very great stress on this statement (Gen. 1:28): “Be fruitful and multiply.” They felt that a special blessing of God rested on this statement; and because they did not multiply, they supposed that they were cursed and under God’s wrath.
Therefore one can easily conclude how severely Rebecca was tortured and how great Isaac’s grief was when he saw that his wife almost despaired of having offspring; for at that time she was about 50 years old. Then she thought: “Now I shall be exhausted and unable to bear children.” Isaac still had some hope. If Rebecca did not bear a child, he would take another wife, just as his father Abraham had done.
Rebecca was deprived of this hope, and she anxiously counted every year and day that had elapsed since she had married Isaac. She wondered whether her years and her age still left her any hope. Therefore this was a far more burdensome trial than the earlier one, for poor Rebecca suspects that she is numbered among those women who have been deprived of the blessing of God. What, then, shall she do, since she sees that she has so anxiously desired offspring in vain? She has been barren for 20 years, and now she is becoming a woman as good as dead; for the year and the time when her womb would be dead were at hand. She undoubtedly asked her husband to pray for her. This one last help she found. She does not want to give him another wife and deprive herself of the glory of motherhood, as Sarah had given her maid Hagar to her husband (Gen. 16:3). Therefore Moses says: “And Isaac prayed to the Lord for his wife.”
But once again the flesh will be offended and will look down on this as ordinary and trivial. For of what importance is it that a husband prays for his barren wife? After all, there are many women who become pregnant without prayer, yes, even contrary to the wish and will of many of them who do not desire to have offspring. But observe that most excellent perseverance, endurance, and expectancy of faith which the flesh does not perceive, and you will find something you will marvel at. For Rebecca could not think about the promise without grief and deep emotion—the promise that descendants should be born from Isaac. While all other women, who neither prayed nor had a promise from God, had been blessed, she alone was living without any hope of offspring and was passing the time of her marriage in great sorrow and tears. Nevertheless, she keeps her faith and with great perseverance urges her husband to intercede for her with the Lord.
If one of us is distressed for so many years by the same kind of affliction or by other misfortunes, by diseases, by exile, and by imprisonment, and does not murmur and does not cast aside his endurance but perseveres firmly in faith and hope, he will see what Rebecca suffered. The flesh considers only the outward things and the things that pertain to the management of the home, namely, that she is engaged in domestic and daily tasks and sleeps with her husband. But it does not see that she has been patient, has sighed, and has wept throughout those entire 20 years; for those most excellent virtues, such as patience, faith, and waiting when the promise of God is delayed, are hidden from the eyes of the world. The flesh gives thought and marvels when it sees a monk in a gray garment, girt with a rope, refraining from eating meat, and yet having none of the faith, the endurance, the affliction, and the things that Rebecca has. Why? Because the world is blind.
But we should accustom ourselves to those conflicts which from time to time, one after another, are usually in store for the godly; and we should learn to believe and persevere, in order that we may not waver and abandon the promise but may be strong and fight against impatience and the fiery darts of the devil (Eph. 6:16), who impels our hearts to grumble and to be angry with God in order that he may destroy our faith and endurance in misfortunes. Let us set before ourselves the example of Isaac and Rebecca. Both waited 20 years, and meanwhile they saw the happiness and the fecundity of the ungodly, who ridiculed them and assailed them with abuse. They said: “Why did he marry that woman and woo a foreigner? Why did he not marry some respectable girl of our own families? Rebecca is done for and is rejected by God.” She undoubtedly heard this sort of abuse, not without great grief in her heart and not without tears, just as Sarah deplored her barrenness and as Hannah mourns pitiably for the same reason (1 Sam. 1:11). Nevertheless she has overcome through patience and the strength of her faith.
We should praise these virtues, and in the accounts of the fathers we should carefully ponder those examples of patience. For this battle against the promise of God is very difficult. Through it ill will, murmuring, and impatience with God’s delaying are overcome. This is characteristic of God, and He is very correctly called “the Expected One.” But we are called “the expectant ones.” These designations should be perpetually observed by our eyes and hearts, in order that we may learn to crush the first impulses, lest we immediately murmur if He delays for one or two or more years what we are looking for. But let us remember that we must persevere and boldly overcome everything that puts our patience to the test, just as Rebecca learned to disdain the insults of other women and of her own domestics until eventually she prevailed over God through her own prayers and those of her husband.
The Hebrew verb עָתַר is very emphatic; for it is a special verb of praying and means “to pray importunately and beyond measure,” in such a way that by knocking and importuning in a vexatious manner we annoy God. We call it “to prevail upon.” First one must ask; in the second place, one must seek; in the third place, one must knock (Matt. 7:7). If we have cried: “Lord, God, help me in this misfortune; deliver me from this evil or from another one,” and immediate deliverance does not follow, then one should look for all the examples of the fathers. “Look, O heavenly Father, how Thou hast aided Thy people at all times.” If He still delays, you should nevertheless not stop praying but should say: “I shall not cease, and I shall not stop knocking; but I shall cry out and knock until the end of my life.” Rebecca exhorted her husband in this manner: “Dear Isaac, do not become weary, and do not give up.” And Isaac saw her tears and sighs, and he prevailed upon the Lord.
Consequently, one should learn from this that when we pray, we are most certainly being heard, just as so far the church has certainly procured peace through prayer and has restrained the Turk together with the pope. Only let us be on our guard lest after we have once begun to pray, we immediately grow weary. But let us seek and let us cast all our care, misfortune, and affliction on God (1 Peter 5:7) and set before Him the examples of every kind of deliverance. Finally let us knock at the door with confidence and with incessant raps. Then we shall experience what James says (5:16): “The prayer of a righteous man has great power”; for it penetrates heaven and earth. God can no longer endure our cries, as is stated in Luke 18:5 about the unjust judge and the widow. But one should not pray only one hour. No, one must cry out and knock. Then you will compel Him to come. Thus I fully believe that if we devote ourselves to prayer earnestly and fervently, we shall prevail upon God to make the Last Day come.
In the same way Rebecca took refuge in earnest and persistent prayer and sighed anxiously night and day. Isaac, too, prayed for her and placed before God nothing else than that one trouble, namely, his wife’s barrenness. We should learn from this that all our troubles, even those that are physical, should be placed before God, but above all the spiritual needs. Isaac prayed in this way: “If it means the hallowing of Thy name, and if it tends to preserve Thy kingdom, give Rebecca offspring.” Where a promise is lacking, as Rebecca lacked it, prayer should supply this and should come to the rescue. But it is a difficult thing and requires great exertion. It is far more difficult than the preaching of the Word or other duties in the church. When we teach, we experience more than we do; for God speaks through us, and it is a work of God. But to pray is a most difficult work. Therefore it is also very rare.
Hence it is something great for Isaac to have the courage to lift up his eyes and hands to the Divine Majesty and to beg, seek, and knock; for it is something very great to speak with God. It is also something great when God speaks with us. But this is more difficult; for our weakness and unworthiness come along and draw us back, so that we think: “Who am I that I should have the courage to lift up my eyes and raise my hands to the Divine Majesty, where the angels are and at whose nod the entire world trembles? Shall I, wretched little man that I am, say to Him: ‘This is what I want, and I beg Thee to give it to me?’ ” The great crowd of the monks and the priests has no knowledge of this; nor do they know what praying is, although some of the godly overcome these thoughts more easily. But really efficacious and powerful prayers, which must penetrate the clouds, are certainly difficult. For I, who am ashes, dust, and full of sins, am addressing the living, eternal, and true God. Therefore it is no wonder that he who prays trembles and shrinks back. Thus long ago, when I was still a monk and for the first time read these words in the Canon of the Mass: “Thou, therefore, most merciful Father,” and also: “We offer to Thee, the living, the true, and the eternal God,” I used to be completely stunned, and I shuddered at those words. For I used to think: “With what impudence I am addressing so great a Majesty, when everybody should be terrified when looking at or conversing with some prince or king!”
But faith, which relies on the mercy and the Word of God, overcomes and prevails over that fear, just as it conquered it in Isaac, who despaired of all human help; for no one is able to help his barren wife. Therefore he takes heart and directs a fervent and powerful prayer to God. Such outstanding boldness and greatness of faith the flesh does not see. But this is written for our sakes, in order that we may be bold and confident, and may learn to pray; for the prayers of believers cannot be in vain. Thus Isaac does not pray in vain either; but, just as Moses says: “And the Lord granted his prayer,” so the Lord will not disregard our sighs and cries either. Only let us be stirred up to pray.
At this point the Jews raise a question about the word נֹכַח. To the Jews it really means “straightforward” or “directly,” stracks für sich, as in Is. 57:2: “Who walks נְכֹחוֹ,” that is who has turned aside neither to the left nor to the right. Accordingly, the Jews maintain that Isaac prayed directly in front of his wife. If it was the common custom to pray in this manner, Rebecca stood directly before him or fell down on her knees, and he placed his hands on her as she wept and sighed. And in this manner they implored the Lord together. If there had been such a rite of praying, the proper meaning of the word could be retained; but if it was not an accepted custom, it has to be explained in a spiritual manner, namely, that he prayed with his whole heart and with concentration on his wife’s misfortune, just as when I pray for someone, I present him to myself in the sight of my heart and see, or think of, nothing else but look upon him alone in my heart.
Thus Isaac prayed while he had his wife before his eyes. In this way Moses wants to point out that it was a fervent and earnest prayer, in which he was not hesitant and did not roam about in his heart and thoughts. A prayer of this kind is praised in the case of the man who had made a bet with Bernard that he would say the Lord’s Prayer without any wandering thoughts. But since they had staked a horse and, in accordance with their agreement, he was forced to confess the truth after finishing his prayer, he confessed that while he was praying, he had been concerned about the saddle and the bridle, whether these had to be added to the horse or not. The prayer of the godly should not be like this, because this prayer is not spoken in a straightforward manner. Instead, the heart wanders now to the right and now to the left. But a true and fervent prayer presents the case to God and with great zeal and fervor directs its attention to this matter alone. It is not disturbed either by any presumption or by any doubt; it says: “Lord God, consider this afflicted little woman and Thy promise.” It neither thinks of nor is concerned about anything else. And this is that unremitting, that is, earnest and straightforward, prayer of a righteous man of which the Epistle of James (5:16) speaks.
 Augustine, Confessions, Book III, chs. 5, 6, pars. 9, 10
 Cf., for example, Crates in The Greek Anthology, Book IX, epigram 497.
 Cf., Luther’s Works, 23, pp. 202-204
 Luther referred to this incident of May 2, 1507, frequently, especially in his Table Talk; it seems to have been on his mind about this time, for he discussed it at table in the summer of 1540 (W, Tischreden, V, Nr. 5357).
 Cf. Lyra ad Gen. 25:21: contra uxorem suam.
 Bernard speaks of impediments to praying the Lord’s Prayer, but not of the wager to which Luther refers here, in his Sermones de tempore, VI, Patrologia, Series Latina, CLXXXIII, 181-183