From Summa Contra Gentiles, III.67 (That God is the cause of operation for all things that operate)
… God is the cause enabling all operating agents to operate. In fact, every operating agent is a cause of being in some way, either of substantial or of accidental being. Now, nothing is a cause of being unless by virtue of its acting through the power of God, as we showed. Therefore, every operating agent acts through God’s power. . . .
it is obvious that every action which cannot continue after the influence of a certain agent has ceased results from that agent. For instance, the manifestation of colors could not continue if the sun’s action of illuminating the air were to cease, so there is no doubt that the sun is the cause of the manifestation of colors. And the same thing appears in connection with violent motion, for it stops with the cessation of violence on the part of the impelling agent. But just as God has not only given being to things when they first began to exist, and also causes being in them as long as they exist, conserving things in being, as we have shown, so also has He not merely granted operative powers to them when they were originally created, but He always causes these powers in things. Hence, if this divine influence were to cease, every operation would cease. Therefore, every operation of a thing is traced back to Him as to its cause.
This passage from Aquinas shows just how wrong Dutch Reformed thinkers like Dooyeweerd and Van Til were to assert that “There is no place anywhere in the whole of Roman Catholic thought for the idea that any human being should be wholly subject to God” (Van Til, Defense of the Faith, 138). Perhaps one could take such thinkers more seriously if Van Til and Dooyeweerd would quote Aquinas himself in their writings – or Copleston’s History of Philosophy, at the least!