The covenant of the pieces, whereby the fortunes of his descendants were revealed to Abraham, was made at a time when he was still childless. As long as Abraham and Sarah dwelt outside of the Holy Land, they looked upon their childlessness as a punishment for not abiding within it. But when a ten years' sojourn in Palestine found her barren as before, Sarah perceived that the fault lay with her. Without a trace of jealousy she was ready to give her slave Hagar to Abraham as wife, first making her a freed woman.
For Hagar was Sarah's property, not her husband's. She had received her from Pharaoh, the father of Hagar. Taught and bred by Sarah, she walked in the same path of righteousness as her mistress, and thus was a suitable companion for Abraham, and, instructed by the holy spirit, he acceded to Sarah's proposal.