Galatians 4:22

You can read about Abraham and his two sons in Genesis Chapter s 15-21. Abraham’s name used to be Abram until God changed it. He had a wife called Sarai. But later God changed her name to Sarah. Sarah had a slave called Hagar. Hagar had a son called Ishmael. Sarah had a son called Isaac. In those days, it was important for a man to have a son. If his wife could not have a son, his wife’s slave could have a son for the man. Slaves had no rights. Sarah considered that Hagar was her property. Sometimes a man would marry a second wife. Their society allowed these actions. God had not given his laws at that time. Now we know that God wants a man to have only one wife (Exodus 20:14; Matthew 5:31-32). A man should stay with his wife even if she cannot have children.