GEN1553 “How is one proven to be a true penitent?” Rabbi Judah asked, and answered: “If the opportunity to commit the same sin presents itself, on two occasions and the sinner does not yield to it” Yoma 86b.   Maimonides expands on this Talmudic teaching: “What constitutes complete repentance? When one is confronted by the identical situation in which he previously sinned and it is within his power to commit the sin again, and he nevertheless does not succumb because he wishes to repent, and not because he is afraid or physically too weak [to repeat the sin].   For example, if he had relations with a woman forbidden to him and after some time, he is alone with her, still in the throes of his passion [literally, ‘in love’] for her, and his virility is unabated, and they are in the same place where they previously sinned; if he [or she] abstains and does not sin, this is a true penitent” Laws of Repentance 2:1. … The fact that Judah, who years earlier had sold his brother into slavery, now offers himself as a substitute for his younger brother is proof to Joseph that Judah’s – and by implication his other brothers’ – repentance is complete.   TELVOL 1:168