REMISSION OF SIN BY THE GIFTS OF GRACE
Sins arise when actions deflect from the right course leading to the end. Since man is conducted to his end not only by natural aids, but by the aids of grace, the sins men commit must be counteracted not by natural aids alone, but also by the helps which grace confers. Contraries exclude each other; therefore, as the aids of grace are taken from man by sin, so sins are forgiven by the gifts of grace. Otherwise man's malice in committing sin would be more powerful in banishing divine grace than the divine goodness is in expelling sin by the gifts of grace.
Furthermore, God's providence over things is in harmony with their mode of being. Changeable things are so constituted that contraries can succeed each other in them; examples are generation and corruption in corporeal matter, and white and black in a colored object. Man is changeable in will as long as he lives his earthly life. Hence man receives from God the gifts of grace in such a way that he is able to forfeit them by sin; and the sins man commits are such that they can be remitted by the gifts of grace.
Besides, in supernatural acts, possible and impossible are regarded from the standpoint of divine power, not from the standpoint of natural power. The fact that a blind man can be made to see or that a dead man can rise, is owing not to natural power but to divine power. But the gifts of grace are supernatural. Therefore a person's capacity to receive them depends on divine power. To say that, once a person has sinned, he cannot receive the gifts of grace, is derogatory to the power of God. Of course, grace cannot co-exist with sin; for by grace man is rightly ordered to his end, from which he is turned away by sin. But the contention that sin is irremissible, impugns the power of God.