Galatians 3:18

Galatians 3:18. For if the inheritance be of the law, it is no more of promise: but God gave it to Abraham by promise.

All through the Book of Genesis, it is promise, promise, and promise. Isaac was an heir of the promise, and Jacob was an heir of the promise. In fact, Isaac was born by promise, and Ishmael the elder brother did not inherit the blessing because he was born after the flesh. They who believe in Christ are heirs according to the promise. Now, a promise takes us out of the region of law.