We proceed to the first article thus:

1. It seems that perfection is not applicable to God. To be perfect means to be made complete, and we cannot say that God is made. Neither then can we say that God is perfect.

2. Again, God is the first beginning of things. Now the beginnings of things appear to be imperfect. The beginning of an animal, or of a plant, for example, is but a seed. It follows that God is imperfect.

3. Again, it was proved in Q.3, Art.4, that God's essence is the same as his existence. But God's existence appears to be very imperfect. It is entirely universal, and therefore receives all things as additional to itself. Hence God is imperfect.

On the other hand: it is said in Matt.5:48: "Be ye therefore perfect, even as your Father which is in heaven is perfect."

I answer: Aristotle tells us that of the ancient philosophers, the Pythagoreans and Leucippus did not ascribe what is best and most perfect to their first principle (12 Metaph., text 40). This was because they believed the first principle to be purely material. A material first principle is very imperfect. Matter, as matter, is potential, and a material first principle is bound to be supremely potential, and therefore exceedingly imperfect. Now God is the first principle, but he is not material. He is defined as efficient cause, and must accordingly be supremely perfect. Just as matter as such is potential, so an agent as such is actual. The first active principle is therefore bound to be superlatively actual, and consequently superlatively perfect. For we say that a thing is perfect in so far as it is actual, and we call a thing perfect when it lacks nothing of its perfection.

On the first point: Gregory says (5 Moral.26, 29): "Let us declare the glory of God by lisping as we can. We cannot rightly say that he is perfect, since he is not made." But since a thing which "becomes" is said to be perfect when it has passed from potentiality to actuality, we borrow the word "perfect" to signify anything which is not lacking in actuality, whether this is achieved through its being made perfect, or otherwise.

On the second point: the material beginning of things around us is imperfect. But it cannot be first absolutely, because it must be derived from something else which is perfect. Even though the seed be the beginning of the animal which develops from it, there is bound to be a previous animal, or plant, from which it came. Something actual must precede the potential, since only what is actual can enable the potential to become actual.

On the third point: existence itself is the most perfect of all things, since it is the actuality of all things. Nothing is actual save in so far as it exists. Existence itself is therefore the actuality of everything, even of forms. It is not a recipient which receives other things. Rather is it that which other things receive. When I speak of the existence of a man, or of a horse, or of anything else, I think of existence as something formal which is received, not as something which can receive existence.