The mercy of God does not suspend the laws of cause and effect. When God forgives me a sin, He destroys the guilt of sin but the effects and the punishment of sin remain. Yet it is precisely in punishing sin that God’s mercy most evidently identifies itself with His justice. Every sin is a violation of the love of God, and the justice of God makes it impossible for this violation to be perfectly repaired by anything but love. Now love is itself the greatest gift of God to men. Charity is our own highest perfection and the source of all our joy. This charity is the free gift of His mercy. Filling us with divine charity and calling us to love Him as He has first loved us and to love other men as He loves us all, God’s mercy makes it possible for us to give full satisfaction to His justice. The justice of God can, therefore, best be satisfied by the effects of His own mercy.
Those who refuse His mercy satisfy His justice in another way. Without His mercy, they cannot love Him. Without love for Him they cannot be “justified” or “made just.” That is to say: they cannot conform to Him Who is love. Those who have not received His mercy are in a state of injustice with regard to Him. It is their own injustice that is condemned by His justice. And in what does their injustice consist? In the refusal of His mercy. We come, then, in the end, to this basic paradox: that we owe it to God to receive from Him the mercy that is offered to us in Christ, and that to refuse this mercy is the summation of our “injustice.” Clearly, then, only the mercy of God can make us just, in this supernatural sense, since the primary demand of God’s justice upon us is that we receive His mercy.
No Man is an Island, pg. 162