Objection 1. It would seem that the end of the government of the world is not something existing outside the world. For the end of the government of a thing is that whereto the thing governed is brought. But that whereto a thing is brought is some good in the thing itself; thus a sick man is brought back to health, which is something good in him. Therefore the end of government of things is some good not outside, but within the things themselves.
Objection 2. Further, the Philosopher says (Ethic. i, 1): "Some ends are an operation; some are a work"--i.e. produced by an operation. But nothing can be produced by the whole universe outside itself; and operation exists in the agent. Therefore nothing extrinsic can be the end of the government of things.
Objection 3. Further, the good of the multitude seems to consist in order, and peace which is the "tranquillity of order," as Augustine says (De Civ. Dei xix, 13). But the world is composed of a multitude of things. Therefore the end of the government of the world is the peaceful order in things themselves. Therefore the end of the government of the world is not an extrinsic good.
On the contrary, It is written (Proverbs 16:4): "The Lord hath made all things for Himself." But God is outside the entire order of the universe. Therefore the end of all things is something extrinsic to them.
I answer that, As the end of a thing corresponds to its beginning, it is not possible to be ignorant of the end of things if we know their beginning. Therefore, since the beginning of all things is something outside the universe, namely, God, it is clear from what has been expounded above (44, 1,2), that we must conclude that the end of all things is some extrinsic good. This can be proved by reason. For it is clear that good has the nature of an end; wherefore, a particular end of anything consists in some particular good; while the universal end of all things is the Universal Good; Which is good of Itself by virtue of Its Essence, Which is the very essence of goodness; whereas a particular good is good by participation. Now it is manifest that in the whole created universe there is not a good which is not such by participation. Wherefore that good which is the end of the whole universe must be a good outside the universe.
Reply to Objection 1. We may acquire some good in many ways: first, as a form existing in us, such as health or knowledge; secondly, as something done by us, as a builder attains his end by building a house; thirdly, as something good possessed or acquired by us, as the buyer of a field attains his end when he enters into possession. Wherefore nothing prevents something outside the universe being the good to which it is directed.
Reply to Objection 2. The Philosopher is speaking of the ends of various arts; for the end of some arts consists in the operation itself, as the end of a harpist is to play the harp; whereas the end of other arts consists in something produced, as the end of a builder is not the act of building, but the house he builds. Now it may happen that something extrinsic is the end not only as made, but also as possessed or acquired or even as represented, as if we were to say that Hercules is the end of the statue made to represent him. Therefore we may say that some good outside the whole universe is the end of the government of the universe, as something possessed and represented; for each thing tends to a participation thereof, and to an assimilation thereto, as far as is possible.
Reply to Objection 3. A good existing in the universe, namely, the order of the universe, is an end thereof; this. however, is not its ultimate end, but is ordered to the extrinsic good as to the end: thus the order in an army is ordered to the general, as stated in Metaph. xii, Did. xi, 10.
Source: Summa Theologica (New Advent)