“And so others said that merits following the effect of predestination are the reason of predestination; giving us to understand that God gives grace to a person, and pre-ordains that He will give it, because He knows beforehand that He will make good use of that grace, as if a king were to give a horse to a soldier because he knows he will make good use of it. But these seem to have drawn a distinction between that which flows from grace, and that which flows from free will, as if the same thing cannot come from both. It is, however, manifest that what is of grace is the effect of predestination, since it is contained in the notion of predestination. Therefore, if anything else in us be the reason of predestination, it will be outside the effect of predestination.” (Summa Theologica, I.23.5)
Obviously contemporary Molinists know Thomas quite well, and the issue is a difficult one that faithful Christians will continue to disagree on. Nevertheless, it seems that this passage gets to the heart of the issue: is grace the effect of God’s predestination, such that our free decision to embrace God has its ultimate cause in Godself, or is it something we must “make use of” in order to be saved?