St Thomas here speaks of moral, not of physical goodness. All creatures are physically good in themselves (Chap. VII); but what is morally good for us is not the mere having and enjoying of this or that particular creature, but the use that we put it to. Possessions perish and change hands: the credit of the use we put them to alone is eternal. Their works follow them (Apoc. xiv, 13).
Of God and His Creatures: 3.134