With respect to the virtues' role in the merit of Christians, St. Thomas says "the merit of eternal life rests chiefly with charity."
Our Lord said (John 14:21): "He that loveth Me, shall be loved of My Father; and I will love him and will manifest Myself to him." Now everlasting life consists in the manifest knowledge of God, according to John 17:3: "This is eternal life: that they may know Thee, the only true" and living "God." Hence the merit of eternal life rests chiefly with charity.Now of course - as we have seen repeatedly - it must be borne in mind that merit comes solely from the grace of God, and that we do not (and cannot) merit eternal life by anything that we do ourselves. So it seems then in this connection that the instrumental means by which grace works this merit in us is by way of the virtue of charity, which itself (as St. Thomas says elsewhere) is a gift of God. So we see here too that our salvation is wholly from God, and not due to ourselves, notwithstanding the mistakes of others.
I answer that, As we may gather from what has been stated above (Article 1 [which we looked at here --RdP]), human acts have the nature of merit from two causes: first and chiefly from the Divine ordination, inasmuch as acts are said to merit that good to which man is divinely ordained. Secondly, on the part of free-will, inasmuch as man, more than other creatures, has the power of voluntary acts by acting by himself. And in both these ways does merit chiefly rest with charity. For we must bear in mind that everlasting life consists in the enjoyment of God. Now the human mind's movement to the fruition of the Divine good is the proper act of charity, whereby all the acts of the other virtues are ordained to this end, since all the other virtues are commanded by charity. Hence the merit of life everlasting pertains first to charity, and secondly, to the other virtues, inasmuch as their acts are commanded by charity. So, likewise, is it manifest that what we do out of love we do most willingly. Hence, even inasmuch as merit depends on voluntariness, merit is chiefly attributed to charity. [ST I-II Q114 A4]
But there is more that seems worth saying here. It seems that the Protestant elevation of faith to the sole principle of justification is directly contrary not merely to what Aquinas says in the present article, but to Scripture. One of the objections to which he replies in I-II Q114 A4 is this:
Further, the greatest principle of merit would seem to be the one whose acts are most meritorious. But the acts of faith and patience or fortitude would seem to be the most meritorious, as appears in the martyrs, who strove for the faith patiently and bravely even till death. Hence other virtues are a greater principle of merit than charity. [Objection 3]To which he replies:
The act of faith is not meritorious unless "faith . . . worketh by charity" (Galatians 5:6). So, too, the acts of patience and fortitude are not meritorious unless a man does them out of charity, according to 1 Corinthians 13:3: "If I should deliver my body to be burned, and have not charity, it profiteth me nothing." [ad 3]More, the apostle writes:
And now there remain faith, hope, and charity, these three: but the greatest of these is charity.How then is charity greater than faith if charity has no role whatsoever (as "sola fide" requires) in salvation? It isn't. Hence it seems that the principle is badly mistaken, out of a misguided though honest interest in avoiding the suggestion that we can work our way to heaven. We can't, and the Catholic Church has never said otherwise. But neither can we see God if we do not have love, sola fide notwithstanding.