Since, as we have seen, Trent has taught that all the causes of our salvation are from God and not from man, there is at least one more observation that may be made. With respect to the question of human merits (as discussed previously), these can only be described as effects of divine grace rather than as causes per se of our salvation. This accords well with what St. Augustine said (as quoted previously):
[W]hat else but His gifts does God crown when He crowns our merits?Think about it. The causes are all from God, says Trent. Consequently our merits as discussed by Trent can only be effects of the divine causes of our salvation. Hence, as St. Augustine says, God crowns his own gifts when he crowns our merits.
Furthermore, it ought to be blindingly obvious that an effect simply cannot call forth its own cause. The very idea is silly! The thunder can't make the lightning; the fire can't strike the match that lights it. And so too we do not merit our salvation in any way that "causes" God to save us, because God is the cause of our salvation just as Trent declares. He is the cause of it in every way. This being the case it is simply ridiculous to claim that Trent repudiated sola gratia.
I think another interesting point can be made, and I was reminded of it while reading Vignaux today (p. 121):
St. Thomas's point of view was the following: 'God by himself can produce all natural effects; that other causes may also produce them is not however superfluous. This does not in fact result from a lack of power, but from an immensity of goodness: as a consequence of goodness, God wished to communicate His resemblance to things, to such a degree that they not only exist, but that they are also in turn causes.' ... His goodness explains why He bestowed efficacy on other beings. To deprive creatures of an activity that is theirs, is to slight the Creator: ... 'To take from things their proper actions is derogatory to divine goodness.' (emphasis in original)Now the subject, properly speaking, of this passage is philosophical; yet the similarities to what we have been discussing seem obvious to me. Just as we have to till the soil (and yet God causes the grain to grow), and just as we must work for a living (and yet every good and perfect gift comes from God, who provides all that we have), so too we must obey our God (and yet He saves us through Christ). Nothing that we do can compel God to cause the wheat to grow. Nothing that we do can compel God to give us the means to provide for our families. Nothing that we do can compel God to sacrifice His Son for us as He did. Our food comes from God. Our homes and other necessaries come from God Our salvation comes from God. And yet he rewards the grace he gives us to love him.
[W]e must believe that nothing further is wanting to the justified, to prevent their being accounted to have, by those very works which have been done in God, fully satisfied the divine law according to the state of this life, and to have truly merited eternal life, to be obtained also in its (due) time, if so be, however, that they depart in grace: seeing that Christ, our Saviour, saith: If any one shall drink of the water that I will give him, he shall not thirst for ever; but it shall become in him a fountain of water springing up unto life everlasting. Thus, neither is our own justice established as our own as from ourselves; nor is the justice of God ignored or repudiated: for that justice which is called ours, because that we are justified from its being inherent in us, that same is (the justice) of God, because that it is infused into us of God, through the merit of Christ. Neither is this to be omitted,-that although, in the sacred writings, so much is attributed to good works, that Christ promises, that even he that shall give a drink of cold water to one of his least ones, shall not lose his reward; and the Apostle testifies that, That which is at present momentary and light of our tribulation, worketh for us above measure exceedingly an eternal weight of glory; nevertheless God forbid that a Christian should either trust or glory in himself, and not in the Lord, whose bounty towards all men is so great, that He will have the things which are His own gifts be their merits (Council of Trent, Session VI, Decree on Justification, Chapter XVI; emphasis added).What we do matters - but when we do good, it is thanks to the grace of God.