What does Genesis 21:13 mean?
Abraham was greatly displeased at the idea of casting his firstborn son Ishmael out of his family and household. God told Abraham to do it anyway, just as Sarah had said. Abraham's name must pass to Isaac, not Ishmael. But God's intent is not to abandon these two to death or poverty.Here, God reassures Abraham once more that He will make a nation of Hagar. She and Ishmael would be provided for and become established. It's the same promise God had previously made both to Hagar (Genesis 16:10) and to Abraham (Genesis 17:20).
Why would God do this for Ishmael? He was Abraham's son, and God had promised to bless Abraham in every way. This included blessing all those related to Abraham. Even though Ishmael was the result of Abraham and Sarah trying to scheme towards their own desires, God still faithfully keeps His promises. Ishmael will not be punished or treated unfairly on account of his parents' dispute.