Paul shows us that Abraham was not justified by his works, since his faith was not earned, but rather reckoned to him, and since we are not reckoned what we are owed, this could not have been something that was owed to Abraham. Moreover, the sacrificial system is not really a way to earn any salvation, since the remission is only a gift from God and not something earned.
Abraham's faith was not a naive faith, either. Hebrews tells us that Abraham knew that since God's promise was to come through Isaac, and that God would have to raise Isaac to fulfill the promise.
Abraham's faith was reckoned to him before his circumcision, which was a seal of the covenant, and thus he is an example of faith for both the Jew and the Gentile. Just as Abraham's faith was reckoned to him, so will it be reckoned to us if we believe.
The closing theme is Gerard Satamian's Chansons Sans Paroles Op. 2 Pastorale, from the album Dry Fig Trees. www.magnatune.com