It can be said that God in the first creation of things decided to produce effects regularly in the presence of, and not in the absence of, certain things and each thing of the same species. And it belongs to these things to be a cause by their nature, i.e., by that nature in which they were constituted at their creation. And the term 'regularly' is used because God did not tie His power down to the creatures.

gabriel biel, whether the sacraments of the new covenant are effective causes of grace p. 4

And so it is not the case that heat is a cause of heat because of some other power that exists in it; rather, it is a cause of heat solely because God has so determined Himself that in the presence of heat-- and not unless it is present--He regularly wills to produce heat. And if He had not so decided, then the very same heat, which would in that case exist without any change, would be heat and yet would not be a cause of heat. Hence, God does nothing through a secondary cause without its being the case that He does it through Himself just as principally and no less so than if He were doing it alone.

gabriel biel, whether the sacraments of the new covenant are effective causes of grace, p.3

This argument seems strong to me and sufficiently plausible for us to conclude that if God were to decide that from this day forward He is going to will to send rain at the utterance of some word pronounced by someone, then that word, once uttered, would be just as properly a cause of the rain brought about by God at its utterance as heat is a cause of heat. And this seems altogether true. For a creature has nothing except from God's will alone, which grants it to the creature freely and contingently.

gabriel biel, whether the sacraments of the new covenant are effective causes of grace, p.3-4