John Calvin Commentary Genesis 16:2

"And Sarai said unto Abram, Behold now, Jehovah hath restrained me from bearing; go in, I pray thee, unto my handmaid; it may be that I shall obtain children by her. And Abram hearkened to the voice of Sarai." — Genesis 16:2 (ASV)

That I may obtain children by her. This is a Hebrew phrase, which signifies to become a mother. Some, however, expound the word as simply meaning to have a son. And certainly בן (ben), which, among the Hebrews, signifies son, corresponds with the verb here used. But since sons are so called metaphorically as being the maintainers of the race, and thus building up the family, therefore, the primary signification of the word is to be retained.

But Sarai claims for herself by right of dominion the child whom Hagar will bring forth, because maidservants do not bring forth for themselves, since they do not have power over their own body. By first speaking to her husband, she does not merely allow a concubine, who would be like a harlot, but introduces and obtrudes one.

And so it appears that when people are wiser in their own eyes than they ought to be, they easily fall into the snare of trying illicit means. Sarai's desire proceeds from the zeal of faith; but because it is not sufficiently subjected to God to wait for His time, she immediately resorts to polygamy, which is nothing other than the corruption of lawful marriage.

Moreover, since Sarai, that holy woman, nevertheless fanned in her husband the same flame of impatience with which she burned, from this we may learn how diligently we ought to be on our guard, lest Satan surprise us by any secret fraud. For not only does he induce wicked and ungodly men to openly oppose our faith, but sometimes, privately and by stealth, he assails us by means of good and simple men, so that he may overcome us unawares. On every side, therefore, we must be on our guard against his wiles, lest by any means he undermine us.

And Abram hearkened to the voice of Sarai. Truly, Abram's faith wavers when he deviates from the word of God and allows himself to be carried away by his wife's persuasion to seek a remedy that was divinely prohibited. He, however, retains the foundation, because he does not doubt that he will, at last, perceive that God is true.

From this example we are taught that there is no reason to despond if, at any time, Satan shakes our faith, provided that the truth of God is not overthrown in our hearts. Meanwhile, when we see Abram, who for so many years had bravely contended like an invincible combatant and had surmounted so many obstacles, now yielding in a single moment to temptation, who among us will not fear for himself in similar danger? Therefore, although we may have stood long and firmly in the faith, we must daily pray that God will not lead us into temptation.