Of God and His Creatures

Reading this passage, any instructed Catholic will see that St Thomas is speaking of that contrition which is called 'perfect,' as being founded on the love of God for His own sake above all things. An act of such contrition delivers the soul from mortal sin at once, before absolution is pronounced, not however without a purpose (in the instructed Catholic) of confession and absolution to follow in due time. The Catholic also knows that an inferior supernatural sorrow, called 'attrition'-- not mentioned in the Contra Gentiles -- is enough, when conjoined with absolution; and to such a case St Thomas tacitly alludes, when he says below: "The case is quite possible of a person at confession receiving grace and forgiveness of the guilt of sin by the power of the keys in the very instant of absolution," i.e., not before then.

Of God and His Creatures: 4.72