From today's missal reading in Philippians 4:10–19:
16] For even when I was at Thessalonica
you sent me something for my needs,
not only once but more than once.
17] It is not that I am eager for the gift;
rather, I am eager for the profit that accrues to your account.
So the Philippian Christians can do things which "profit" their "account" as Christians. Here is the Greek for verse 17:
 οὐχ ὅτι ἐπι ζητῶ τὸ δόμα, ἀλλὰ ἐπιζητῶ τὸν καρπὸν τὸν πλεονάζοντα εἰς λόγον ὑμῶν.
The word for "account" is lógon (which is mildly humorous, since in our day we must "log in to an account" or "log on to the Internet"), and you can read the Strong's Lexicon here to understand more about the word. You can also examine the other uses of the word in the New Testament, based on Strong's Concordance here. Granted the word does not strictly mean a "bank account," but rather an explanation of one's behavior when faced with judgment. This is the reason accounts have taken on their financial connotation: they are detailed records (explanations) of previous fiscal behavior that must be assessed (judged) by a higher authority. The upshot is that St Paul is commending the Philippian believers for adding to their account before God by means of their acts of charity towards him. At the Final Judgment, Paul assures them, their charity will abound to (pleonázonta, cf. Perseus Lexicon) their account before God.
Now, the typical Reformed objection to the idea of merit is that, at the Final Judgment, the believer will give an account simply by pointing to the Lamb, or showing the Blood. And this is true as far as it goes. The problem, however, is that Jesus is the Lamb who takes away sin, and the Blood is what washes away our guilt––not the Lamb who specifically performs the acts of virtue to which He calls us, and not the Blood which paints on our virtues. The atonement is a negative victory for us: it gets us out of Hell. It does not however completely suffice to determine our precise standing in the Eschaton, a standing which is but a ratification of the "account" we have before God. On the one hand, our merits in Christ are our merits, but, on the other hand, they are ultimately meritorious before God only becuase they are in Christ.
I grant that from today's reading it does not logically follow that our vices can detract from the atoning power of the Blood of the Lamb, but I do think it adds striking support to the notion of merit as taught by the Church. As we read in Part 3, Section 1, Chapter 3, Article 2, subsection III of the Catholic Catechism:
2006 The term "merit" refers in general to the recompense owed by a community or a society for the action of one of its members, … deserving reward or punishment. Merit is relative to the virtue of justice, in conformity with the principle of equality which governs it.
2007 With regard to God, there is no strict right to any merit on the part of man. Between God and us there is an immeasurable inequality, for we have received everything from him, our Creator.
2008 The merit of man before God in the Christian life arises from the fact that God has freely chosen to associate man with the work of his grace. The fatherly action of God is first on his own initiative, and then follows man's free acting through his collaboration, so that the merit of good works is to be attributed in the first place to the grace of God, then to the faithful. Man's merit, moreover, itself is due to God, for his good actions proceed in Christ, from the predispositions and assistance given by the Holy Spirit.
2009 Filial adoption, in making us partakers by grace in the divine nature, can bestow true merit on us as a result of God's gratuitous justice. This is our right by grace, the full right of love, making us "co-heirs" with Christ and worthy of obtaining "the promised inheritance of eternal life."60 The merits of our good works are gifts of the divine goodness.61 "Grace has gone before us; now we are given what is due. . . . Our merits are God's gifts."62
2010 Since the initiative belongs to God in the order of grace, no one can merit the initial grace of forgiveness and justification, at the beginning of conversion. Moved by the Holy Spirit and by charity, we can then merit for ourselves and for others the graces needed for our sanctification, for the increase of grace and charity, and for the attainment of eternal life. …
A second Reformed maneuver in light of such "works" passages in Scripture is to localize, or 'immediatize', their meaning. In this case, the rebuttal would be that Paul is merely talking about the standing the Philippians have in the eyes of other Christians, or perhaps the impression their kindness toward him makes on non-Christians. But this is specious for at least two reasons. First, regarding the impact charity has on non-Christians, the biblical theme of "fearing God, not man" makes it highly suspect that Paul would encourage believers to curry favor with non-believers. Granted, Jesus tells the disciples to let their light shine before men (Matthew 5) so that they may glorify the Father, but this actually reinforces the Catholic notion that faith by itself is inadequate: what truly glorifies God is the concrete expression of that faith. (It also undermines the Reformed doctrine of monergism, since if salvation unfolds monergistically, it is incoherent for Jesus to exhort believers to "let" their light shine, as if they could synergistically impede or abet the power of God.) Second, if St Paul is applauding the account the Philippians have in the eyes of other churches, he is again undermining Reformed doctrine since he is commending the works of believers as a means to justify themselves. Further, if acts of virtue, supernaturally inspired though they may be, are "as but filthy rags" before God, then it is a strange logic on the part of the "Reformed Paul" to base his congratulations on filthy rags.
The last-ditch Reformed rebuttal is that while "saving faith" just is faith that tends to produce good works, it is still only faith which saves us. This, however, is simply to concede the Catholic teaching, the point of which is that "faith alone," devoid of actual virtuous output, is insufficient for salvation.