God promised Abram that his wife Sarai would have a son. But Abram, instead of believing God, slept with his servant Hagar. Thus, Ishmael was born. No matter how much Abram pleaded, God would not use Ishmael to fulfill his covenant promise to Abram. Instead, Sarai did conceive, and gave birth to Isaac.
This story warns us to believe God and not to try to fulfill his promises in what we think is our own ability, but what is really sin. Abram sinned against God, his wife, and Hagar. Because of Abram's unbelief, Ishmael and Hagar suffered homelessness and beating. Likewise, if you sin against God, others will suffer, God's name will be shamed, and the exercise of God's will on the earth will be compromised. Will you forever forsake the way of Ishmael, and trust Jesus, who loved you so much that he died for you?