Teshuva and Aveira Lishma

 Rav Tzadok (Takanas Hashavim 9) Through repentance willful transgressions are transformed into inadvertent errors or even merits; it constitutes a rectification of the past—specifically regarding actions already carried out—achieved by bringing one’s heartfelt repentance all the way to the root of the soul within the intellect reaching the Throne of Glory, from which the rectification of those past actions also emanates. The reason such acts are likened to inadvertent errors—specifically through repentance born of fear—is analogous to the case of one who intends to eat pork but ends up eating lamb: the Talmud likens this to an inadvertent error regarding forgiveness and atonement, because the person’s intent was to commit a forbidden act. Thus, even though the past is rectified—with everything transformed into merits, as all is the will of God and there is no evil at all "for You are with me"—nevertheless, if the original intent was to transgress, the act is still classified as an inadvertent error. Therefore it is necessary to rectify the intent until it is viewed entirely as a merit and not at all as a sin even though we know the original intent was to sin and do evil.