Commenting on Colossians 1:16 Thomas says:
He [Paul] says that the Son is the first-born of every creature because he is generated or begotten as the principle of every creature. And so he says, for in him all things were created.
With respect to this, we should note that the Platonists affirmed the existence of Ideas, and said that each thing came to be by participating in an Idea, like the Idea of man, or an Idea of some other kind. Instead of all these we have one, that is, the Son, the Word of God. For an artisan makes an artifact by making it participate in the form he has conceived within himself, enveloping it, so to say, with external matter; for we say that the artisan makes a house through the form of the thing which he has conceived within himself. This is the way God is said to make all things in his wisdom, because the wisdom of God is related to his created works just as the art of the builder is to the house he has made. Now this form and wisdom is the Word; and thus in him all things were created, as in an exemplar: “He spoke and they were made” (Gen 1), because he created all things to come into existence in his eternal Word.