Thomas Aquinas

“ On the contrary, What is granted in accordance with a fair judgment, would seem a condign reward. But life everlasting is granted by God, in accordance with the judgment of justice, according to 2 Tim. 4:8: "As to the rest, there is laid up for me a crown of justice, which the Lord, the just judge, will render to me in that day." Therefore man merits everlasting life condignly.
I answer that, Man's meritorious work may be considered in two ways: first, as it proceeds from free-will; secondly, as it proceeds from the grace of the Holy Ghost. ”

“ Now the manner and measure of human virtue is in man from God. Hence man's merit with God only exists on the presupposition of the Divine ordination, so that man obtains from God, as a reward of his operation, what God gave him the power of operation for, even as natural things by their proper movements and operations obtain that to which they were ordained by God; differently, indeed, since the rational creature moves itself to act by its free-will, hence its action has the character of merit, which is not so in other creatures. ”

“ Thus if a man receives a horse from his master, he merits it by a good use of it in his master's service. Now God is much more bountiful than man. Much more, therefore, may a man, by subsequent works, merit the first grace already received from God.
On the contrary, The nature of grace is repugnant to reward of works, according to Rom. 4:4: "Now to him that worketh, the reward is not reckoned according to grace but according to debt." Now a man merits what is reckoned to him according to debt, as the reward of his works. Hence a man may not merit the first grace. ”

“ But if we suppose, as indeed it is a truth of faith, that the beginning of faith is in us from God, the first act must flow from grace; and thus it cannot be meritorious of the first grace. Therefore man is justified by faith, not as though man, by believing, were to merit justification, but that, he believes, whilst he is being justified ”

“ If it is considered as regards the substance of the work, and inasmuch as it springs from the free-will, there can be no condignity because of the very great inequality. But there is congruity, on account of an equality of proportion: for it would seem congruous that, if a man does what he can, God should reward him according to the excellence of his power. ”

“ 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. ”

“ Again, congruous merit, whereby one merits the first grace for another, is prevented from having its effect on account of the impediment of sin in the one for whom it is merited. Much more, therefore, is the efficacy of such merit impeded by the obstacle which is in him who merits, and in him for whom it is merited; for both these are in the same person. And therefore a man can nowise merit for himself restoration after a fall. ”

“ Now everlasting life is a good exceeding the proportion of created nature; since it exceeds its knowledge and desire, according to 1 Cor. 2:9: "Eye hath not seen, nor ear heard, neither hath it entered into the heart of man." And hence it is that no created nature is a sufficient principle of an act meritorious of eternal life, unless there is added a supernatural gift, which we call grace. ”

“ Hence we must say that if temporal goods are considered as they are useful for virtuous works, whereby we are led to heaven, they fall directly and simply under merit, even as increase of grace, and everything whereby a man is helped to attain beatitude after the first grace. For God gives men, both just and wicked, enough temporal goods to enable them to attain to everlasting life ”

“ But one may merit the first grace for another congruously; because a man in grace fulfils God's will, and it is congruous and in harmony with friendship that God should fulfil man's desire for the salvation of another, although sometimes there may be an impediment on the part of him whose salvation the just man desires. ”

“ Hence it is clear that the perseverance of glory which is the term of the aforesaid movement falls under merit; but perseverance of the wayfarer does not fall under merit, since it depends solely on the Divine motion, which is the principle of all merit. ”

“ Therefore, if we speak of man in the first state, there is only one reason why man cannot merit eternal life without grace, by his purely natural endowments, viz. because man's merit depends on the Divine pre-ordination. ”

“ The impetration of prayer rests on mercy, whereas condign merit rests on justice; hence a man may impetrate many things from the Divine mercy in prayer, which he does not merit in justice, according to Dan. ”

“ And therefore it is clear that no one can merit condignly for another his first grace, save Christ alone; since each one of us is moved by God to reach life everlasting through the gift of grace; hence condign merit does not reach beyond this motion. But Christ's soul is moved by God through grace, not only so as to reach the glory of life everlasting, but so as to lead others to it, inasmuch as He is the Head of the Church, and the Author of human salvation, according to Heb. ”

“ Without grace a man cannot have a work equal to a work proceeding from grace, since the more perfect the principle, the more perfect the action. But the objection would hold good, if we supposed the operations equal in both cases. ”

“ Now man by his nature is ordained to beatitude as his end; hence, too, he naturally wishes to be blessed. Hence man by his natural endowments and without grace can merit beatitude which is eternal life. ”

“ Now no act of anything whatsoever is divinely ordained to anything exceeding the proportion of the powers which are the principles of its act; for it is a law of Divine providence that nothing shall act beyond its powers. ”

“ We are unprofitable servants; we have done that which we ought to do." Therefore a man can merit nothing from God.
Objection 2: Further, it would seem that a man merits nothing from God, by what profits himself only, and profits God nothing. ”

“ Further, that would seem to fall under merit, which God bestows on anyone for a service done. But God sometimes bestows temporal goods on men for services done for Him. For it is written (Ex. 1:21) : "And because the midwives feared God, He built them houses"; on which a gloss of Gregory (Moral. xviii, 4) says that "life everlasting might have been awarded them as the fruit of their goodwill, but on account of their sin of falsehood they received an earthly reward." And it is written (Ezech. 29:18) : "The King of Babylon hath made his army to undergo hard service against Tyre . ”