God’s promise. God made a promise to Abraham and that happened long before the law was given to Moses. Read Galatians 3:15-18.
Brethren, I speak in terms of human relations: even though it is only a man’s covenant, yet when it has been ratified, no one sets it aside or adds conditions to it. Now the promises were spoken to Abraham and to his seed. He does not say, “And to seeds,” as referring to many, but rather to one, “And to your seed,” that is, Christ. What I am saying is this: the Law, which came four hundred and thirty years later, does not invalidate a covenant previously ratified by God, so as to nullify the promise. For if the inheritance is based on law, it is no longer based on a promise; but God has granted it to Abraham by means of a promise.
Galatians 3:15-18 NASB
The promise was given to Abraham and to Jesus Christ who fulfilled it. However, the Jews had gotten bogged down by the law and forgotten the importance of the promise. This is where the faith of Abraham is more life-changing for us than the law of Moses. Are we following in the faith or still trying to cling to the law?