Abraham had listened to God and it had been credited to him as righteousness. His listening, believing, and obeying had given him the right standing with God. He had a relationship with God Almighty.
Abraham has been promised innumerable children. They are just a future hope. In his current situation, what he sees with his eyes, is that he has no children. He knows he’s getting older too. He’s about 85. His eyes and human understanding are telling him something’s wrong. He may not have vocalized it, but he’s well aware of God not fulfilling His promise. While he still believes in the promise, he doesn’t trust God to bring it about. He decides to stop waiting on God, to stop waiting on the promise to be fulfilled. He’s going to help things along.
Sarah isn’t willing to wait on God either. Sarah has the bad idea to have Abraham take her maid Hagar to have a child with. He does and she does have a baby. When she’s pregnant, Hagar stops acting humbly toward her mistress, Sarah. Sarah is jealous and angry. It has been shown that Sarah’s the problem; she’s the reason they haven’t had children. At least, she thinks that’s been shown. Sarah’s having all sorts of feelings and breaks down and treats Hagar harshly.
The baby is named Ishmael, “God hears.” He is a child of Abraham and receives the promise of growing into an innumerable people. However, this isn’t the promised child for the promised land. It is spoken over him that his people will always be against others and others will always be against them. Not a people of peace. This turmoil was brought into the world because Abraham listened to a voice other than the voice of God. He had listened; he had obeyed; he had been blessed. Now, instead of trusting in God’s firm promise, he listens to another. He obeys his wife’s suggestion. He acts as if God is not going to act. He acts like He has to take matters into his own hands. He acts like God is not reliable.
And so a people of partial promise is born, a people of torment. Ishmael has Abraham for his father, but he isn’t chosen by God. He has the blessing of becoming a great people, but misses out on the promised land, missing out on being called the people of promise, on being called God’s chosen people. It all started with listening to the wrong voice.