(CG 2/15). That God is to all things the Cause of their being (Book 2: God The Origin of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

To every effect produced by God there is either something pre-existent or not. If not, the thesis stands, that God produces some effect out of nothing pre-existent. If anything pre-exists, we either have a process to infinity, which is impossible, or we must come to something primitive, which does not presuppose anything else previous to it. Now this primitive something cannot be God Himself, for God is not the material out of which anything is made (B. I, Chap. XVI): nor can it be any other being, distinct from God and uncaused by God (Chap. XV).

3. The more universal the effect, the higher the cause: for the higher the cause, the wider its range of efficiency. Now being is more universal than motion. Therefore above any cause that acts only by moving and transmitting must be that cause which is the first principle of being; and that we have shown to be God (B. I, Chap. XIII). God therefore does not act merely by moving and transmuting: whereas every cause that can only bring things into being out of pre-existing material acts merely in that way, for a thing is made out of material by movement or some change.

4. It is not proper to the universal cause of being, as such, to act only by movement and change: for not by movement and change is being, as such, made out of not-being, as such, but 'being this' is made out of 'not being this.' But God is the universal principle of being (Chap. XV). Therefore it is not proper to Him to act only by movement or change, or to need pre-existent material to make anything.

5. Every agent has a term of action like itself, for its acts inasmuch as it is in actuality. Given then an agent in actuality by some form inherent in it, and not to the whole extent of its substance, it will be proper to such an agent to produce its effect by causing a form in some way inherent in matter. But God is in actuality, not by anything inhering in Him, but to the whole extent of His substance (B. I, Chap. XVIII). Therefore the proper mode of divine action is to produce the whole subsistent thing, and not a mere inherent thing, as is form in matter.

10. Between actuality and potentiality such an order obtains, that, though in one and the same being, which is sometimes in potentiality sometimes in actuality, potentiality is prior in time to actuality (although actuality is prior in nature), yet, absolutely speaking, actuality must be prior to potentiality, as is clear from this, that potentiality is not reduced to actuality except by some actual being. But matter is being in potentiality. Therefore God, first and pure actuality, must be absolutely prior to matter, and consequently cause thereof.

This truth divine Scripture confirms, saying: In the beginning God created heaven and earth (Gen. i,1). For to create is nothing else than to bring a thing into being without any pre-existent material.

Hereby is confuted the error of the ancient philosophers, who supposed no cause at all for matter, since in the actions of particular agents they always saw some matter pre-existent to every action. Hence they took up the common opinion, that nothing is made out of nothing, which indeed is true of the actions of particular agents. But they had not yet arrived at a knowledge of the universal agent, the active cause of all being, whose causative action does not necessarily suppose any pre-existent material.