I contend that you will struggle to find any teaching in the OT that commends polygamy. It is one of those things that sounds good, until it isn’t. And by then, it’s too late. Sarah, having given up hope of having children, decided to make her Egyptian slave Abraham’s second wife, and her surrogate. It sounded good, until it wasn’t. And by then, it was too late. When pregnant, Hagar had thoughts above her station and Sarah’s mistreatment of her made her flee into the desert. Poor Hagar was caught up in Sarah’s ‘Plan-B.’ But ‘God heard her’ in the wilderness. He dispatched the angel of the Lord, who named her son, described his character, and sent her back to Sarah. Genesis 16:16 tells us that “Abram was eighty-six years old when Hagar bore Ishmael to him.” When Isaac was born 14 years later, any previously perceived value attributed to Ismael’s existence by Sarah disappeared. He was tolerated until he ‘mocked’ his brother, Isaac, and then he and his mother were banished from the tents of Abraham. At death’s door, again ‘God heard,’ and saved them both, promising: “I will make him into a great nation” (Gen.21:18). And “God was with the boy as he grew up” (Gen.21:20). At the end of the day Hagar was a blessed matriarch of 12 tribal leaders (Gen.25:16) and Ishmael choose a life contrary to that of his brother Isaac as “a wild donkey of a man” (Gen.16:12). God had met Abraham’s sadness over his son’s banishment by returning Abraham to the beginning. To the point of the original promise that God had made before he and Sarah decided to help God along: “It is through Isaac that your offspring [seed=Jesus] will be reckoned” (Gen.21:12). Ishmael, God assured him, would become a nation because he was Abraham’s son (v.13). God’s plan was set from the start. Helping God ‘get it right,’ set into motion problems for all parties concerned that should have never been. Try taking God at His Word.