Although he doesn’t even have one son, in Genesis 15, God covenants with Abraham that his descendants will be as numerous as the stars.
But then in our prophecy from Genesis 22, God narrows this down to make him a Promise about only One. To help us connect the dots and embrace the wonder of this, consider the words the Spirit moved Paul to express:
The promises were spoken to Abraham and to his seed. Scripture does not say “and to seeds,” meaning many people, but “and to your seed,” meaning one person, who is Christ. Galatians 3:16 NIV