An excerpt from a Gloss within Introduction to Philosophical Principles:
Among the most popular arguments against the existence of God is the imperfection of the universe: the argument that not only are our lives on earth messy—at times through no fault of our own as either individuals or even as a species, as when a hurricane decimates our town or a plague sweeps the country, depriving us of health, security, loved ones, employment, food, etc.—but in fact the whole universe appears messy: continually subject to destructions, calamities, every integrity of every life, every system, every organized whole being under threat at every moment.
But this, in fact, is the strangest and least-reflective sort of anthropocentrism: the kind that insists the universe should not only be centered around human beings, but centered around the desires of human beings—as though our desires were an infallible guide for what ought to happen, when our own history is a clear and obvious argument that our desires are anything but infallible. That such an argument would occur to any mind speaks of either habitual self-indulgence (or an attitude which would so indulge, in other circumstances) or vague and confused theoretical beliefs concerning “justice” and “goodness”. At the core of such confusion is a belief that, if there is a Creator God, that God owes to us a certain debt—that by being created, we are owed anything at all is refuted by Aquinas in his c.1259/65: Summa contra Gentiles, lib.2, c.28-29.
Rather, if there is any “justice” in God’s act of creation, it is a “justice” of “propriety”: not that the creation attains a certain standard of desirability for the creatures within it, but that the creation is fitting to the goodness of the creator (c.1259/65: SCG, 2.28, n.13). Thus there is a kind of consequent justice: in that, having created a universe, the whole of the universe ought to be structured such that what is right can occur for each part; each part ought to be fitting disposed to the others; and each part of each individual ought to be fitting disposed to the whole of which it is a part (c.1259/65: SCG, 2.29, n. 17):
This necessity which is from what is posterior in being although prior in nature, is not an absolute necessity, but conditional; that is [the kind of necessity we see in situations such as], “if this ought to happen, then it is necessary this first come to be.” According to this kind of necessity, it follows that there is found a threefold debt in the production of creatures. First, from the whole of things in the universe there arises a conditional indebtedness to every part, which is required for the perfection of the universe. For if the universe is made by the will of God, it ought to be made such that He should make the sun and the moon, and such things without which the universe would not be able to be. Second, there arises a conditional indebtedness from one creature to another; as, if animals and plants are made by the will of God to be, it is suitable that He should make the heavenly bodies, by which such things are conserved; and if He willed humans to be, it is necessary to make the plants and the animals, and other such things of this kind which humans require for a perfected existence; although these and other such things were made by God from His pure will. Third, a conditional indebtedness arises for the sake of every creature from its parts, properties, and accidents, on which the creature depends as to its existence or as to some perfection thereof; as, supposed that God willed to man humans, there occurs a debt from this supposition that He conjoin the soul and the body, and supply the senses, and other such aids, both intrinsic and extrinsic. In all such matters, if they are rightly considered, God is not said to owe the creature anything, but rather to the fulfillment of His own disposition.
Necessitas autem quae est a posteriori in esse licet sit prius natura, non est absoluta necessitas, sed conditionalis: ut, si hoc debeat fieri, necesse est hoc prius esse. Secundum igitur hanc necessitatem in creaturarum productione debitum invenitur tripliciter. Primo, ut sumatur conditionatum debitum a tota rerum universitate ad quamlibet eius partem quae ad perfectionem requiritur universi. Si enim tale universum fieri Deus voluit, debitum fuit ut solem et lunam faceret, et huiusmodi sine quibus universum esse non potest. Secundo, ut sumatur conditionis debitum ex una creatura ad aliam: ut, si animalia et plantas Deus esse voluit, debitum fuit ut caelestia corpora faceret, ex quibus conservantur; et si hominem esse voluit, oportuit facere plantas et animalia, et alia huiusmodi quibus homo indiget ad esse perfectum; quamvis et haec et illa ex mera Deus fecerit voluntate. Tertio, ut in unaquaque creatura sumatur conditionale debitum ex suis partibus et proprietatibus et accidentibus, ex quibus dependet creatura quantum ad esse vel quantum ad aliquam sui perfectionem: sicut, supposito quod Deus hominem facere vellet, debitum ex hac suppositione fuit ut animam et corpus in eo coniungeret, et sensus, et alia huiusmodi adiumenta, tam intrinseca quam extrinseca, ei praeberet. In quibus omnibus, si recte attenditur, Deus creaturae debitor non dicitur, sed suae dispositioni implendae.
Now it may seem, to the unbeliever—or to the anti-believer who has adopted the jaded position—that this makes God cruel; that the ordination of parts in a universe rife with suffering and chaos as part of God’s will reveals a malicious God. This, again, is to view the universe through the anthropocentric lens of desire. To denounce all suffering and pain and disorder as evidence of an evil God (or the absence of a God) is to view these occurrences from a myopic point of view, and not with a consideration of the whole universe.
While a full consideration of these topics could only be engaged in a study of metaphysics—the principles being beyond our ken here—it is recommended for those interested in the topic (the perfusion of the universe with purpose) to read c.1259/65: SCG, lib.2, c.45, especially n.7-9, and 1266-68: ST Ia, q.47-48.