Very good point. I have known about this for quite a while, but didn't have the gumption to type it all out. We can agree that Romans 4:3 demonstrates Abraham to have been justified through the gift of faith he received from God. The Catholic Church acknowledges what the text clearly says: "Abraham believed God and it was reckoned to him as righteousness," referencing Genesis 15:6.
There is more to this text, however, than many of our non-Catholic friends know. While the Catholic Church agrees that Abraham was justified by faith in Genesis 15:6 as Paul said, we also note that Abraham was justified at other times in his life as well, indicating justification to have another aspect to it. Again, there is a sense in which justification is a past action in the life of believers, but there is another sense in which justification is revealed to be a process as well.
Abraham was depicted as having saving faith in God long before Genesis 15:6. Abraham had already responded to Gods call in Genesis 12 with what is revealed to be saving faith, years before his encounter with the Lord in Genesis 15. In addition, Abraham is revealed to have been justified again in Genesis 22, years after Genesis 15, when he offered his son Isaac in sacrifice in obedience to the Lord.
Genesis 12:14: Now the Lord said to Abraham, "Go from your country and your kindred and your fathers house to the land that I will show you
" So Abram went, as the Lord had told him. Compare Hebrews 11:6,8: And without faith it is impossible to please God
By faith Abraham obeyed when he was called
and he went out, not knowing where he was to go.
Genesis 15:4,6: "This man [a slave] shall not be your heir; your own son shall be your heir." And [Abram] believed the Lord: and he reckoned it to him as righteousness. Compare Romans 4:3: For what does the scripture say? "Abraham believed God, and it was reckoned to him as righteousness."
Genesis 22:15-17: And the angel of the Lord called to Abraham a second time from heaven, and said, "By myself I have sworn, says the Lord, because you have done this, and have not withheld your son, your only son, I will indeed bless you, and I will multiply your descendents as the stars of heaven
because you have obeyed my voice." Compare James 2:21-22,24: Was not Abraham our father justified by works, when he offered his son Isaac upon the altar?
faith was completed by works
You see that a man is justified by works and not by faith alone.
The Bible tells us Abraham had faith way back in Genesis 12. And according to Hebrews 11:6-8, this was not a natural faith analogous to the faith the demons have (see James 2:19), but rather a supernatural and saving faith given as a gift from God. If Abraham was not justified until Genesis 15:6, how could he already have saving faith in Genesis 12? In addition, if Abraham was justified once and for all in Genesis 15:6, why did he need to be justified again in Genesis 22 according to James 2:21? The reason is simple: According to these texts, justification is revealed in Scripture to be a process rather than a mere one-time event.