Whether sins once forgiven return through a subsequent sin?

❌ Objection 1 : It would seem that sins once forgiven return through a subsequent sin. For Augustine says (De Bapt. contra Donat. i, 12): "Our Lord teaches most explicitly in the Gospel that sins which have been forgiven return, when fraternal charity ceases, in the example of the servant from whom his master exacted the payment of the debt already forgiven, because he had refused to forgive the debt of his fellow-servant." Now fraternal charity is destroyed through each mortal sin. Therefore sins already taken away through Penance, return through each subsequent mortal sin.

❌ Objection 2 : Further, on Lk. 11:24, "I will return into my house, whence I came out," Bede says: "This verse should make us tremble, we should not endeavor to explain it away lest through carelessness we give place to the sin which we thought to have been taken away, and become its slave once more." Now this would not be so unless it returned. Therefore a sin returns after once being taken away by Penance.

❌ Objection 3 : Further, the Lord said (Ezech. 18:24): "If the just man turn himself away from his justice, and do iniquity . . . all his justices which he hath done, shall not be remembered." Now among the other "justices" which he had done, is also his previous penance, since it was said above (Question [85], Article [3]) that penance is a part of justice. Therefore when one who has done penance, sins, his previous penance, whereby he received forgiveness of his sins, is not imputed to him. Therefore his sins return.

❌ Objection 4 : Further, past sins are covered by grace, as the Apostle declares (Rm. 4:7) where he quotes Ps. 31:1: "Blessed are they whose iniquities are forgiven, and whose sins are covered." But a subsequent mortal sin takes away grace. Therefore the sins committed previously, become uncovered: and so, seemingly, they return.