The perfect is known by a certain negation- it is that to which nothing can be added or taken away. In our experience, this consists in the thing being limited- that is, something lacks pefection if it goes beyond the limit, or if it falls short of it. Call this limited perfection, which in our experience is the only kind of perfection there is.
But we can also understand that perfection could occur if the the perfect being had a certain infinity, for if something is unlimited, it is also something to which nothing could be added or taken away. This is shown even in the material and imperfect infinity of mathematics: to add or subtract anything from infinity leaves one with infinity.
These are two different meanings of perfection, one limited and the other unlimited. Though we are using one word “perfection” to speak of both, the word is not a genus to which limited and unlimited are species, the way that “tree” can be said of oak and maple. Rather, from the first idea of perfection “that to which nothing can be added…” we notice another meaning of “what cannot be added to”. The same word means two different things, and yet the meaning of the first leads us by the hand to the meaning of the other. Perfection means something different when said of the unlimited and the limited, and yet we still need to understand the first meaning of perfection before we can understand the second one.