Read Galatians 3:17 Using Other Translations
And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect.
This is what I mean: the law, which came years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.
This is what I am trying to say: The agreement God made with Abraham could not be canceled 430 years later when God gave the law to Moses. God would be breaking his promise.