The Father William Most Collection
Merit is a claim to a reward. No creature by its own power can generate a claim on God. A claim can take place only if God makes a covenant or promise, saying, in effect," If you do this, I will do that."
The redemption has several aspects. A major one is that it is a new covenant. In a covenant, God says, in effect, "If you do this, I will do that". Cf. Exodus 19:5:"If you really hearken to my voice and keep my covenant, you will be my special people."
Jeremiah foretold the new covenant in 3l:31 ff. Vatican II in Constitution on the Church § 9 said Jesus made the new covenant the night before He died. He took bread here, wine there, and said: "This is my body... this is my blood". This was a seeming separation of body and blood, standing for death. It was as if He said to the Father: "Father, I know the command you have given me. I am to die tomorrow. Very good, I turn myself over to death - expressed by this seeming separation - I accept, I obey." The next day He carried out that pledge.
So it is He who merited, established a claim to all forgiveness and grace by His obedient death (cf. Romans 5:19 and Vatican II, On the Church §3).
St. Paul makes clear that we are saved if and to the extent that we are members of Christ, and like Him. An essential feature of likeness to Him is in joining in His obedience to the Father, particularly at the renewal of the new covenant in the Mass (Cf. Vatican II, On Liturgy § 10).
So by being a member of Christ and being like Him, we get in on the claim He generated. We do not do this alone or by ourselves. This is a merit or a claim.
But we become members of Christ without earning it, that is, without merit. St. Paul insists over and over in Galatians and Romans that we are justified by faith, we receive the first grace, or justification, gratis: cf. Romans 3. 24-26: "being justified gratuitously by His grace."
The reception and possession of this first grace constitutes a claim to heaven, inasmuch as we are members of Christ, and coheirs with Him (Romans 8:17). As sons of God and brothers of Christ we have a claim to inherit the kingdom.
Therefore to sum up: 1) e get first grace without earning it (cf. Council of Trent, DS 1532). 2) The possession and reception of this grace gives us a claim, or merit:Council of Trent DS 1582.
Can we merit for others? Not in the strict sense. The claim we described is strictly personal by very nature: by being members of Christ and like Him we get in on the claim He generated. However we can do something similar. In Col 1. 24: "Now I rejoice in my sufferings for you, and I fill up the things that are lacking to the afflictions of Christ, in my flesh, for His body, which is the Church."
Now of course, there was nothing lacking to the sufferings of Christ - that is, in Christ considered as an individual. But there is the whole Christ, i.e., Head and members. St. Paul tells us in Rom 8. 17: "We are fellow heirs with Christ, provided we suffer with Him, so we may also be glorified with Him." (This is the theme of syn Christo, of being saved and sanctified if and to the extent that we are members of Christ, and like Him. (More of this in St. Paul in Rom 8. 9; Rom 6. 1-6; Col 3. 1-4; Eph 2. 5-6).
So it is not enough to say: Christ paid infinitely for our sins. He did. But the Father wills that we be like Him, to be capable of receiving what He earned (the syn Christo theme again). If we are not, then we are incapable to receiving
But some members of Christ do not do their part, that is they do not do their part in filling this divine condition. But, thanks to the unity of the Mystical Body, one member can make up for another. St. Paul believed it as his role, especially as Apostle, to help make up for the deficiencies of others. He was glad to do that.
Therefore we too can do something to make up for the deficiencies of others.
God on His part is more than willing to grant all graces to others. But they may be not open, may even be resisting. They may be hardened or blinded, by repeated grave sin.
So we can make up for them, but if a person is hardened or blinded, then it takes an extraordinary grace to cut through the resistance or keep it from developing. Such a grace is extraordinary by nature (cf. the file on extraordinary grace for explanation). It is extraordinary since when God cuts through resistance, He is not just letting that person's freedom take its course. Normally it is the human who makes the first decision on whether or not a grace comes in vain (cf. 2 Cor 6. 1). But God can, not routinely - for that would be making the extraordinary to be ordinary - grant a grace that will still convert such a soul. But precisely since it is extraordinary, extraordinary prayer and penance is needed on the part of another to get that grace. We think of the case of St. Augustine's mother, who did prayer and penance for years to obtain his conversion. He surely was very hardened.
This is also the reason why Our Lady at Fatima is supposed to have asked for prayer and penance, saying: many are lost because there is no one to do such a thing for them. They would not do it for themselves, for they are blinded and hardened. So it is only someone else who can and will do it.