Why is the distinction between Isaac and Ishmael important?

The difference between Isaac and Ishmael is significant in understanding the nature of God's covenant with Abraham. Ishmael, born out of Abraham’s and Sarah’s attempt to fulfill God's promise through their own efforts, was not the promised child. In contrast, Isaac was born through divine intervention to a woman who was barren, illustrating that God's promises are fulfilled according to His purpose and timing. This distinction underscores the Reformed understanding of election, where God chooses whom He will bless, demonstrating that the covenant is based on God's grace rather than human will or works, as elaborated in Romans 9:10-13.