Objection 1. It would seem that temporal goods fall under merit. For what is promised to some as a reward of justice, falls under merit. Now, temporal goods were promised in the Old Law as the reward of justice, as appears from Deuteronomy 28. Hence it seems that temporal goods fall under merit.
Objection 2. 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 (Exodus 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 (Ezekiel 29:18): "The King of Babylon hath made his army to undergo hard service against Tyre... and there hath been no reward given him," and further on: "And it shall be wages for his army... I have given him the land of Egypt because he hath labored for me." Therefore temporal goods fall under merit.
Objection 3. Further, as good is to merit so is evil to demerit. But on account of the demerit of sin some are punished by God with temporal punishments, as appears from the Sodomites, Genesis 19. Hence temporal goods fall under merit.
Objection 4. On the contrary, What falls under merit does not come upon all alike. But temporal goods regard the good and the wicked alike; according to Ecclesiastes 9:2: "All things equally happen to the just and the wicked, to the good and to the evil, to the clean and to the unclean, to him that offereth victims and to him that despiseth sacrifices." Therefore temporal goods do not fall under merit.
I answer that, What falls under merit is the reward or wage, which is a kind of good. Now man's good is twofold: the first, simply; the second, relatively. Now man's good simply is his last end (according to Psalm 72:27: "But it is good for men to adhere to my God") and consequently what is ordained and leads to this end; and these fall simply under merit. But the relative, not the simple, good of man is what is good to him now, or what is a good to him relatively; and this does not fall under merit simply, but relatively.
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; and thus these temporal goods are simply good. Hence it is written (Psalm 33:10): "For there is no want to them that fear Him," and again, Psalm 36:25: "I have not seen the just forsaken," etc.
But if these temporal goods are considered in themselves, they are not man's good simply, but relatively, and thus they do not fall under merit simply, but relatively, inasmuch as men are moved by God to do temporal works, in which with God's help they reach their purpose. And thus as life everlasting is simply the reward of the works of justice in relation to the Divine motion, as stated above (3,6), so have temporal goods, considered in themselves, the nature of reward, with respect to the Divine motion, whereby men's wills are moved to undertake these works, even though, sometimes, men have not a right intention in them.
Reply to Objection 1. As Augustine says (Contra Faust. iv, 2), "in these temporal promises were figures of spiritual things to come. For the carnal people were adhering to the promises of the present life; and not merely their speech but even their life was prophetic."
Reply to Objection 2. These rewards are said to have been divinely brought about in relation to the Divine motion, and not in relation to the malice of their wills, especially as regards the King of Babylon, since he did not besiege Tyre as if wishing to serve God, but rather in order to usurp dominion. So, too, although the midwives had a good will with regard to saving the children, yet their will was not right, inasmuch as they framed falsehoods.
Reply to Objection 3. Temporal evils are imposed as a punishment on the wicked, inasmuch as they are not thereby helped to reach life everlasting. But to the just who are aided by these evils they are not punishments but medicines as stated above (Question 87, Article 8).
Reply to Objection 4. All things happen equally to the good and the wicked, as regards the substance of temporal good or evil; but not as regards the end, since the good and not the wicked are led to beatitude by them.
And now enough has been said regarding morals in general.
Source: Summa Theologica (New Advent)