To give a human example, brothers: even with a man-made covenant, no one annuls it or adds to it once it has been ratified. Now the promises were made to Abraham and to his offspring. It does not say, “And to offsprings,” referring to many, but referring to one, “And to your offspring,” who is Christ. This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void. For if the inheritance comes by the law, it no longer comes by promise; but God gave it to Abraham by a promise.
So writes Paul in Galatians, chapter 3. But he is arguing against circumcision which did not come 430 years later. It was given to Abraham. So in Romans 4, Paul doesn’t spend as much time contrasting Abraham to Moses as he does contrasting Abra[ha]m in Genesis 15 to Abraham in Genesis 17:
Is this blessing then only for the circumcised, or also for the uncircumcised? We say that faith was counted to Abraham as righteousness. How then was it counted to him? Was it before or after he had been circumcised? It was not after, but before he was circumcised. He received the sign of circumcision as a seal of the righteousness that he had by faith while he was still uncircumcised. The purpose was to make him the father of all who believe without being circumcised, so that righteousness would be counted to them as well, and to make him the father of the circumcised who are not merely circumcised but who also walk in the footsteps of the faith that our father Abraham had before he was circumcised. For the promise to Abraham and his offspring that he would be heir of the world did not come through the law but through the righteousness of faith. For if it is those of the law who are to be the heirs, faith is null and the promise is void. For the law brings wrath, but where there is no law there is no transgression.
In that last sentence, Paul jumps the 430 years. But the rest of it is all about the shift that occurred within the time frame of Abraham’s own life.