I want to consider the meaning of the term “justice,” which in common usage implies “to render to every man his due,” according to the famous expression of Ulpian, a Roman jurist of the third century. In reality, however, this classical definition does not specify what “due” is to be rendered to each person. What man needs most cannot be guaranteed to him by law. In order to live life to the full, something more intimate is necessary that can be granted only as a gift: we could say that man lives by that love which only God can communicate since He created the human person in His image and likeness. Material goods are certainly useful and required – indeed Jesus Himself was concerned to heal the sick, feed the crowds that followed Him and surely condemns the indifference that even today forces hundreds of millions into death through lack of food, water and medicine – yet “distributive” justice does not render to the human being the totality of his “due.” Just as man needs bread, so does man have even more need of God. Saint Augustine notes: if “justice is that virtue which gives every one his due ... where, then, is the justice of man, when he deserts the true God?” (De civitate Dei, XIX, 21).And he concludes:
What then is the justice of Christ? Above all, it is the justice that comes from grace, where it is not man who makes amends, heals himself and others. The fact that “expiation” flows from the “blood” of Christ signifies that it is not man’s sacrifices that free him from the weight of his faults, but the loving act of God who opens Himself in the extreme, even to the point of bearing in Himself the “curse” due to man so as to give in return the “blessing” due to God (cf. Gal 3, 13-14). But this raises an immediate objection: what kind of justice is this where the just man dies for the guilty and the guilty receives in return the blessing due to the just one? Would this not mean that each one receives the contrary of his “due”? In reality, here we discover divine justice, which is so profoundly different from its human counterpart.
God has paid for us the price of the exchange in His Son, a price that is truly exorbitant. Before the justice of the Cross, man may rebel for this reveals how man is not a self-sufficient being, but in need of Another in order to realize himself fully. Conversion to Christ, believing in the Gospel, ultimately means this: to exit the illusion of self-sufficiency in order to discover and accept one’s own need – the need of others and God, the need of His forgiveness and His friendship.... Thanks to Christ’s action, we may enter into the “greatest” justice, which is that of love (cf. Rm 13, 8-10), the justice that recognises itself in every case more a debtor than a creditor, because it has received more than could ever have been expected.It would be interesting to explore the relation of these comments to the whole twentieth-century debate about nature and grace. For he is talking here about what is "due" to man, and that debate was about how we might think that man has no purely natural "end" - since he can arrive at union with God only through the free gift of grace - and yet simultaneously maintain the truth that we have no "right" to that grace, as though we could demand it as our due. The Pope seems to be saying that the answer lies in the difference between human and divine justice. Man has no right to expect more than his "natural" due, and yet God would hardly be God if he did not love us in a way that gives infinitely more than that. In God, justice seems to converge and even coincide with mercy.