The Justification of Abraham: Commentary on Romans 4:4-5
Abraham's belief in God's promise is a God-pleasing virtue that includes, therefore, a formation of charity and hope towards God. It constitutes a faith that, for the ungodly, is a repentant faith. For the saint, a firm commitment to persevere with God's plan over and against falling to the temptation to go one's own way. Therefore, the faith of Abraham does indeed serve to be an interior sanctity that God recognizes as the "obedience of faith". Nevertheless, God credits more to Abraham than what his faith gives to God. We have to keep in mind that St. Paul sees in the justification act upon Abraham the justification of a man who is, whatever else might be said that was praiseworthy up to this point (Rom. 4:18-22), ungodly. Therefore, in the imputation of Abraham's faith as righteousness, something of a merciful grace is being applied. He is not just recognizing the value of Abraham's faith as meriting justification, i.e., the remission of sins and the sanctifying renewal of the interior man. Let's say again that Abraham's faith does not give to God something equal or congruous with the value of the "righteousness" wherewith God reckoned to him. God gives something more to Abraham than Abraham gives to God.
In fact, infinitely more. The accreditation of faith as righteousness entails the counting towards Abraham the infinite payment of Christ's blood for the remission of sins. To wipe the slate of our guilt clean takes infinitely more than the theological virtues (infused faith, hope, and love). It required God's own blood to satisfy for. This is why the labor-debt paradigm does not pertain to Abraham's justification. Not because faith is being pictured as a wholly non-contributory and worthless instrument in the transaction of imputation, but because the infusion of repentant faith (faith formed by love which disposes the will to serve God), which is a divine gift impossible for human nature anyway, can never be a sufficient congruity wherewith to earn the remission of sins, regardless of its being an instrument of justification. So as pleasing as repentance and faith is to God, as much a necessary condition for justification that it is, and as truly ontological that the infused righteousness is in the resultant disposition to love and serve God is, neither repentance nor faith can rise to the infinite price required to pay for our sins.
However, contrary to Protestant readers of Romans 4:4-5, the "gift of infused faith" does truly form a cause to what it means to be justified in that faith is formed by love, making the soul truly devoted to God in obedience. And it also thereby has a reason why God applies the infinite worth of Christ's blood. It is not as if faith is an empty and worthless instrument to receive the righteousness of Another.
This interpretation is proven by the next example given by Paul in King David (Psalm 32) who speaks of the forgiven man as the man to whom God imputes righteousness apart from meritorious works. You have the need of repentant faith (faith formed by love) which, although not meriting the remission of sins, is nevertheless a required condition for the application of the infinite cost of Christ's blood to wipe away our sins.