Any discussion surrounding the issue of justification ought to, like all fruitful discussions, begin with defining our terms. The first act of the mind is apprehension and intellectual grasping of what is being discussed. We must first agree on the meaning of the terms we are going to be using before we can argue about them. In my experience, Catholics and Protestants use the term justification without actually saying what they mean by it. They proceed to argue operating under the assumption that they are using the terms univocally. Often, however, this is not the case. A clear definition at the outset goes a long way in helping the two sides not argue past one another.
Justification
Justification only makes sense when we properly recognize what amounts to, according to Aristotle, an insurmountable obstacle. He thought friendship with the gods was impossible because it can only occur between equals. Man as a mere creature is incapable of true friendship with God unless he is somehow made equal with God. He can never enter into a personal relationship with God unless He freely elevates man. The term justification has a juridical tone to it, but in truth this is not essentially a legal problem. It has nothing do with sin per se, but really is just man’s default position as a creature. Sin has just complicated the issue for sure, but the problem would exist even if sin didn’t. Thus the Council of Trent, in response to the Protestant teachings on justification, said that one is changed by justification “from an unjust person into a just person and from an enemy into a friend of God.”
Elevation from man’s natural state to a supernatural state that makes him capable of friendship with God is a free gift. That ought to be obvious from what has been said. We call this gift grace. But there is a problem with using this term; namely that grace is a broad term that requires a modifier. This is where it is helpful to have a strong Catholic vocabulary. Grace, broadly speaking, falls into two categories: actual grace and sanctifying grace.
Grace
Actual grace is the interior assistance that God confers upon mankind in order to render him capable of supernatural acts of the soul. In other words, it is God’s help to us in doing works that make us worthy of eternal life. These works can be antecedent in the sense that when a man is in need of conversion or returning back to God from sin, he is given supernatural assistance in doing so. They can also be consequent, a topic we will return to in a moment. What actual graces do is enlighten the mind to recognize the true Good that is friendship with God and/or strengthen the will to move to repentance. What is equally important is that these graces require man’s cooperation—friendship can be offered but never coerced. God is responsible for bestowing them, but man is still responsible for responding to them.
Sanctifying grace on the other hand “is a habitual gift, a stable and supernatural disposition that perfects the soul itself to enable it to live with God, to act by his love. Habitual grace, the permanent disposition to live and act in keeping with God’s call, is distinguished from actual graces which refer to God’s interventions, whether at the beginning of conversion or in the course of the work of sanctification” (CCC 2000).
It is, once again, a free gift but it is this free gift that renders us capable of friendship with God. By making us “partakers of the divine nature,” sanctifying grace infuses the divine life into our souls and elevates us to a supernatural plane. In other words, we truly become like God. Our first parents were created with this free gift (made in the image and likeness) but lost it during the Fall (thus only in the image of God). Now, rather than having it bestowed on us in birth, it is bestowed on us in re-birth. The ordinary way that it is given to us is through Baptism. We are “born from above” (Jn 3:7) in Baptism and adopted as true children of God. Baptism gives to us a likeness to God—like Father, like son.
It bears mentioning as well a word about Heaven. We tend to treat Heaven as “other-wordly” and simply as a reward. That is true as far as it goes, but it doesn’t necessarily go far enough. Heaven is really the place where the friends of God see Him face to face. It is only those who have remained His friends that are capable of seeing Him as He is (1 Jn 3:2). This is why we speak of the necessity of remaining in a “state of grace.” Only those who die with sanctifying grace in their soul can avoid being destroyed by God, “Who is a consuming fire” (Heb 12:29). In other words, only those whom God has made holy, not just imputed holiness to, but who actually are holy, can endure His presence.
Merit
Despite the fact that we speak of justification as a free gift, we also speak of merit. This term seems to imply a debt on God’s part. This sounds suspiciously like “we can earn our salvation” and so people tend to shut down when we use the term. An important reminder helps to clear up some of the confusion. Naturally good acts remain just that, natural. They remain in the natural realm and have their reward here and now. We are capable of doing many good acts on our own. What we are incapable of doing are supernatural acts. Even those who are in a state of grace cannot do these action. They require actual grace and must proceed from a supernatural motive. Christ says both “without Me you can do nothing” (actual grace) and promises reward for the works that are performed for His sake (c.f Mk 9:40 “Anyone who gives you a cup of water to drink because you belong to Christ, amen, I say to you, will surely not lose his reward.”).
Although we require the assistance of actual grace in performing these supernatural acts, God still imputes them to us as though they were done by us. He rewards our cooperation in them because it shows our desire to love Him and in so doing actually increases that love within us. This is what St. Paul is referring to when he tells the Corinthians that “But by the grace of God I am what I am, and his grace to me has not been ineffective. Indeed, I have toiled harder than all of them; not I, however, but the grace of God [that is] with me” (1 Cor 15:10). It is not unlike a father who gives his son money so that he may buy a Christmas present for his father. He is pleased not because of the gift but because of the heart from which the gift came.
Merit again is not just a legal term but a way to describe how we grow to be more like God. These acts are completely outside of our natural capacity, but once elevated to the supernatural realm, we become capable of doing them. God is the initiator, we are the secondary instruments. Notice how this explanation helps to sidestep the whole faith and works controversy which quickly develops into a conversational wormhole. Knowing these terms can help us avoid this apologetical pitfall.