The Lutheran Aquinas.

I recently ran across this quote from Saint Thomas on justifying grace. I think it sums up really well the catholic understanding of grace, which does not overwhelm or destroy our nature, but raises and perfects it.

God does not justify us without ourselves, because while we are being justified we consent to God’s justification by a movement of our free will. Nevertheless this movement is not the cause of grace, but the effect; hence the whole operation pertains to grace. (Summa,I-II, q. 111, a.2, ad.2)

Catholic Christianity rejects both the Pelagian idea of an autonomous will, and determinism. For Aquinas, just as much as for Luther, salvation is grace through and through, but while Luther seems (at least at times) to have believed that any human cooperation meant a diminishment of grace, Aquinas believed that the human will moved by God, could genuinely cooperate. Not to use Luther's words against him, but I think in this case "his thoughts of God were too human," and he seems to have placed God's causality on the same level as ours. I think St. Thomas helps us out of many of the knottier problems of Protestant theology on this point.