Old guilt not rusting

AELW 6:377

"We must be on our guard against sins with all zeal and watchfulness, for they never depart with impunity unless the punishments are removed by very earnest repentance and God’s mercy. Otherwise it is a case of old guilt not rusting. Moreover, when dangers are impending, we pray: “O God, do not avenge old guilt; do not remember our iniquities, O Lord.” Simeon and Levi sin quite freely, and for a time the sin lies dormant. But it is sleeping at the door (cf. Gen. 4:7) so that sometime later it may be aroused for punishment. Then it is suddenly present and bites so that the sinner cries out: “O wretched man that I am! I have merited this punishment by some sin or another. Alas! This is what I learned thereby.” Here sin is a horrible and sad matter, carrying punishment from God with it, especially if we do not judge ourselves, just as, on the other hand, our good deeds never lack their own rewards."