As stated in Genesis 15, Abram and Sarai did not have any children. If you recall, in Genesis 13, God told Abram that if the dust of the earth could be numbered, then his descendants can be numbered. In Genesis 15, God told Abram that if he could number the stars, so shall his descendants be. So, God is promising that Abram will have numerous descendants. Remember in Genesis 12, he is already 75 years old. Presuming that Abram and Sarai were a couple with great communication skills, I am guessing that he told her about God’s promise of numerous descendants. Sarai had an Egyptian maidservant by the name of Hagar. Sarai said to Abram that the Lord kept her from bearing children so she told Abram to go be intimate with her maid, Hagar and perhaps she would obtain children by Hagar. Abram heeded the voice of Sarai. At this point, did God ask Sarai for her help to manifest His promise? Was Abram a little “henpecked” since he heeded the voice of his wife? Or, was this just a “man thin