Before men, therefore, who have been justified in this manner,-whether they have preserved uninterruptedly the grace received, or whether they have recovered it when lost,-are to be set the words of the Apostle: Abound in every good work, knowing that your labour is not in vain in the Lord; for God is not unjust, that he should forget your work, and the love which you have shown in his name; and, do not lose your confidence, which hath a great reward.
Having been justified by the grace of God through Jesus Christ – as the Decree makes clear is the only way that one may obtain justification – we ought to live lives of obedience to God; and God rewards these good works.
And whosoever shall give to drink to one of these little ones a cup of cold water only in the name of a disciple, amen I say to you he shall not lose his reward. [Mt. 10:42]
Whatsoever you do, do it from the heart, as to the Lord, and not to men: Knowing that you shall receive of the Lord the reward of inheritance. [Col. 3:23-24]
Do not therefore lose your confidence which hath a great reward. [Heb. 10:35, quoted above in §16 of the Decree]
For God is not unjust, that he should forget your work and the love which you have shown in his name, you who have ministered and do minister to the saints. [Heb. 6:10, quoted above in §16 of the Decree; note that because justice has to do with paying what is due to another, the clear implication is that some sort of reward has been merited]
Many (Most?) Protestants don't like to concede this, but the simple fact is that what Christians do has a bearing in eternity.
Now it is at this point that the most adamant enemies of the Catholic Faith will start stamping around and braying "Legalism!" But when they do this, they have stopped reading much too soon; indeed, one wonders if they stop deliberately at this point. Because the Fathers of Trent continue:
And, for this cause, life eternal is to be proposed to those working well unto the end, and hoping in God, both as a grace mercifully promised to the sons of God through Jesus Christ, and as a reward which is according to the promise of God Himself, to be faithfully rendered to their good works and merits. For this is that crown of justice which the Apostle declared was, after his fight and course, laid up for him, to be rendered to him by the just judge, and not only to him, but also to all that love his coming [2Tim 4:7-8 – RdP]. For, whereas Jesus Christ Himself continually infuses his virtue into the said justified,-as the head into the members, and the vine into the branches,-and this virtue always precedes and accompanies and follows their good works, which without it could not in any wise be pleasing and meritorious before God,-we 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.
That righteousness in Christians that God rewards is not their own as though it came from themselves, as Trent says; rather, it comes from God, so that God is rewarding that which he himself has given. This might be familiar to longtime readers of this blog (if such actually exist! Ha!), since it is exactly what St. Augustine says about the matter of God rewarding our merits:
[W]hat else but His gifts does God crown when He crowns our merits?