‘Now Sarai, Abram's wife bore him no children, and she had a handmaid, an Egyptian whose name was Hagar. And Sarai said to Abram, “Look, now, Yahweh has restrained me from bearing. Go in, I beg you, to my handmaid. It may be that I will obtain a child by her”.'
Sarai knows of God's promises to Abram, the covenant promises. But she has reached the age when it is unlikely she will have a child. As time passes she grieves for the dilemma of her husband. She has an Egyptian handmaid, probably one of those given to Abram by Pharaoh, and she proposes that Abram has a child by her handmaid and that they adopt the child as Abram's heir.
She is aware what it has meant to Abram not to have an heir, and as they grow older together she is concerned to give him satisfaction. What she proposes was in accordance with custom, and it will remove her shame. It was an accepted practise that a wife's servant, being her slave and not her husband's, could bear a child for her through her husband, and because the slave was hers the child was hers also. If a natural son was born later many examples elsewhere allow for him to replace the adopted son.
Thus the tablets from ancient Nuzi give an interesting near-parallel to this practise - ‘If Gilimninu (the bride) will not bear children, Gilimninu shall take a woman of N/Lulluland (where the best slaves came from) as a wife for Shennima.' The slave woman would improve in status but would remain of inferior status to the real wife. (Compare Genesis 30:3; Genesis 30:9 - there the slave woman bears ‘on the knees' of her mistress. That is, her child will be her mistress's).
Nuzi dates later than Genesis (15th Century BC), but similar records have been recovered from other earlier sites such as Ur, Kish, Ebla, Alalakh, Mari and Boghazkoi. However although there there was the similar practise of a barren wife arranging for a slave to bear a child for her elsewhere, it was not necessarily always the case, for regularly the husband could take his own action, or simply adopt a slave. But the way used by Sarai preserved the wife's pride and possibly gave her greater rights.
A subsidiary wife and her child could in many cases not be sent away (compare Genesis 16:6; Genesis 21:10-11), although there is an example where it is said that the freedom obtained by expulsion compensates for the action.
But while these practises do confirm the authenticity of the background to the narratives, they cannot be used for dating, as such customs continued unchanged for hundreds of years, and varied between groups.
Genesis 16:2-3 (2c-3)
‘And Abram listened to the voice of Sarai. And Sarai, Abram's wife took Hagar the Egyptian, her handmaid, after Abram had dwelt in the land of Canaan for ten years, and gave her to Abram her husband to be his wife.'
Abram has shown great consideration for his wife by not acting on his own. Probably his confidence in Yahweh has caused him to delay action up to this point. He had probably hoped for a son by Sarai. Here it is stressed that the initiative now comes from Sarai, and at his wife's insistence he yields. He knows it is important for his wife to have a protector in the future, and wants her to be satisfied in her heart.
“Ten years”. A round number not to be taken literally. It means ‘a good number of years' (compare ‘ten times' - 31:41). Probably the idea is that they have been in the land of promise without a birth resulting and the ‘ten years' indicates a sufficient and justifiable length of time to justify secondary action in order to produce an heir, descended from Abram, as God had promised.
The twofold stress on the fact that Hagar is an Egyptian is possibly intended to make us look back and remember the first time that Abram pre-empted God, in Egypt. There too his faith faltered.