Such is the mysterious statement asserted by St. Thomas. Does it mean that
1. God delights in or enjoys contemplating more the better things?
2. God gives greater reward to better people?
3. God wills more good to certain people and therefore and because of this those people turn out to be better?
Hmm… God probably does enjoy through union by love human happiness, feeling with us. True happiness is the ultimate indication of goodness. Therefore (1) is probably true.
(2) and (3) each on its own is a considerable exaggeration. It is not the case either that God alone bestows good upon a man; or that man alone creates his own good.
For example, grace requires nature. But grace is the beginning of glory in us. So, glory, too, requires nature (and grace). Now God’s happiness lies in His own self. Human happiness is in external goods, especially God. (Well, the loving union is for both lovers. So, the vine and the branches are to an extent one, not so much as Jn 14:9 and Jn 10:30 but plenty good.) But enjoyment of God requires perfection of character; indeed, one sense of glory is clarity, lack of any desire to hide anything about oneself in shame. Character is built by means of earnest cooperation of man and God.
It is sometimes objected that “reward” seems mechanical: you push a lever and a piece of cheese drops down. Nothing so crude needs to be held: God simply agrees to give His own company and familial love to the blessed. That’s the only reward to be postulated.
But a man must make himself suitable for enjoying this good. A wicked person will not have fun in heaven. Hence, man’s own self-making.
The reward is the same: God. The capacity to enjoy God, to be happy, differs among men. Inequality is due to human complementarity not any arbitrariness or “respecting of persons” on the part of God. Inequality of nature and accidents and human doings and goings begets further inequalities of grace. Again, maximum possible grace (consistent with the good of the whole) is always given, but that maximum is different for every person at every moment in time. Thus, these differences are due to man’s own struggles and God’s taking every opportunity, as if an entrepreneur, to help.
(2) and (3) must then be paired and rightly understood.