A very simple pre-Christmas lesson. You cannot heal your mortal wounds yourself, for an offence that is infinite requires infinite power.
1 On the same basis, it can be shown that man cannot revive from mortal sin except through grace.
2 For by mortal sin man is turned away from his ultimate end. But man is not ordered to his ultimate end except by grace. Therefore, by grace alone can man revive from sin.
3 Again, an offense can be removed only by love. But through mortal sin man offends God, for it is said that “God hates sinners” (see Wis. 14:9; Sirach 12:3, 7), inasmuch as He wills to deprive them of the ultimate end which He makes ready for those whom He loves. So, man cannot revive from mortal sin except through grace, whereby a certain friendship is developed between God and man.
4 For this purpose, also, all the arguments given above for the necessity of grace could be brought forward.
5 Hence, it is said in Isaiah (43:25): “I am He who blots out your iniquities for My own sake”; and in the Psalm (84:3): “You have forgiven the iniquity of Your people; You have covered all their sins.”
6 By this we set aside the error of the Pelagians, who said that man can rise from sin by his free will.