161 Now, Sarai, Abram’s wife, had not borne him children. She had an Egyptian slavegirl named Hagar. 2 Sarai said to Abram, “The Lord has kept me from bearing children. Pray, come to bed with my slavegirl. Perhaps I will be sonned through her.” Abram listened to the voice of Sarai.
3 Sarai, Abram’s wife, took Hagar the Egyptian, her slavegirl, after Abram was settled for ten years in the land of Canaan, and gave her to her husband, Abram, as a wife. 4 He came to bed with Hagar, and she became pregnant. When she realized that she was pregnant, her mistress was lowered in her eyes. 5 Sarai said to Abram, “This wrong is your fault. I put my slavegirl in your lap, and when she saw she was pregnant, she lost respect for me. May YHWH see justice done between me and you!”
6 Abram said to Sarai, “Look, she’s your slavegirl; do whatever seems good to you.” Sarai bullied her, and she fled from Sarai.
Having participated in a dramatic ritual beyond becoming blood brothers, that contained a threat if it is broken, a question about the promise of offspring needs to be considered—what happens if G*D’s side of the bargain is not kept? Best to not overthink this and proceed to help G*D out by all possible means.
Immediately after this bloody, flaming, ritual, we are reminded that Sarai remains childless. Speculation is available at all times, and this moment in particular. Abram had not been sworn to secrecy about the ritual; did he tell Sarai about it? If so, she may have decided this promise-business had gone on long enough and it was time for her to do her part—step away and place her slavegirl on Abram’s lap herself.
Sarai is quite thorough in her actions. Presumably, there is another ritual that now happens when Hagar is promoted to Abram’s wife. Some translations bowdlerize this action by calling Hagar a concubine rather than a wife, but the Hebrew uses the same terms for Hagar as was used to describe Sarai at the beginning of the chapter—“wife.”
All is well and good in theory. When Hagar conceives, relationships change. Who’s the real “wife” now? Sarai feels slighted, diminished, demoted. Hagar has usurped the process of inheritance. Abram’s family tree will have Hagar as the main branch and Sarai as a dried-up side twig.
Sarai had been put aside as a “wife” once already, in Egypt. Now she is set aside as a “wife” who could not bear Abram a son (remember this is a patriarchal story).
Having contrived a situation, Sarai now complains about it. Coming to Abram, Sarai brings an ultimatum beyond rituals and promises—“Choose, now, whether I remain your wife!” We do not know what went into Abram’s response beyond Sarai’s famous beauty and years of common experience. All we know is that Abram washed his hands and left Hagar in Sarai’s. Whereupon, Sarai bullied Hagar until she fled into a deadly desert as the last best choice left her.