Objection 1. It would seem that the world is not governed by anyone. For it belongs to those things to be governed, which move or work for an end. But natural things which make up the greater part of the world do not move, or work for an end; for they have no knowledge of their end. Therefore the world is not governed.
Objection 2. Further, those things are governed which are moved towards an object. But the world does not appear to be so directed, but has stability in itself. Therefore it is not governed.
Objection 3. Further, what is necessarily determined by its own nature to one particular thing, does not require any external principle of government. But the principal parts of the world are by a certain necessity determined to something particular in their actions and movements. Therefore the world does not require to be governed.
On the contrary, It is written (Wisdom 14:3): "But Thou, O Father, governest all things by Thy Providence." And Boethius says (De Consol. iii): "Thou Who governest this universe by mandate eternal."
I answer that, Certain ancient philosophers denied the government of the world, saying that all things happened by chance. But such an opinion can be refuted as impossible in two ways.
First, by observation of things themselves: for we observe that in nature things happen always or nearly always for the best; which would not be the case unless some sort of providence directed nature towards good as an end; which is to govern. Wherefore the unfailing order we observe in things is a sign of their being governed; for instance, if we enter a well-ordered house we gather therefrom the intention of him that put it in order, as Tullius says (De Nat. Deorum ii), quoting Aristotle [Cleanthes].
Secondly, this is clear from a consideration of Divine goodness, which, as we have said above (44, 4; 65, 2), was the cause of the production of things in existence. For as "it belongs to the best to produce the best," it is not fitting that the supreme goodness of God should produce things without giving them their perfection. Now a thing's ultimate perfection consists in the attainment of its end. Therefore it belongs to the Divine goodness, as it brought things into existence, so to lead them to their end: and this is to govern.
Reply to Objection 1. A thing moves or operates for an end in two ways.
First, in moving itself to the end, as man and other rational creatures; and such things have knowledge of their end, and of the means to the end.
Secondly, a thing is said to move or operate for an end, as though moved or directed by another thereto, as an arrow directed to the target by the archer, who knows the end unknown to the arrow. Wherefore, as the movement of the arrow towards a definite end shows clearly that it is directed by someone with knowledge, so the unvarying course of natural things which are without knowledge, shows clearly that the world is governed by some reason.
Reply to Objection 2. In all created things there is a stable element, at least primary matter; and something belonging to movement, if under movement we include operation. And things need governing as to both: because even that which is stable, since it is created from nothing, would return to nothingness were it not sustained by a governing hand, as will be explained later (104, 1).
Reply to Objection 3. The natural necessity inherent in those beings which are determined to a particular thing, is a kind of impression from God, directing them to their end; as the necessity whereby an arrow is moved so as to fly towards a certain point is an impression from the archer, and not from the arrow. But there is a difference, inasmuch as that which creatures receive from God is their nature, while that which natural things receive from man in addition to their nature is somewhat violent. Wherefore, as the violent necessity in the movement of the arrow shows the action of the archer, so the natural necessity of things shows the government of Divine Providence.
Source: Summa Theologica (New Advent)