The Midrash here reminds us how easy it is to concoct justifications for even that which is unquestionably wrong.
The Midrash (Bereishit Rabba 85:2), cited by Rashi (39:1), comments that Potifar’s wife had “altruistic” motives for trying to lure Yosef into an intimate relationship. She foresaw through astrology that she and Yosef would have shared offspring, and so she felt justified in pursuing an adulterous affair with him. In truth, this prediction referred to her daughter, Osnat, who would later marry Yosef (41:45).
It has been suggested that the Midrash’s intent is to magnify the intensity of the test which Yosef confronted at this time. He not only faced strong physical temptation to sin, but also had a way of possibly justifying the sinful act in his mind. Resisting temptation is always difficult, but less so when one is firm in his conviction and has a clear sense of right and wrong. Once the act in question can somehow be justified and even seem altruistic, the inner defenses are weakened and the person becomes especially vulnerable. Yosef thus had to resist temptation despite hearing the astrological predictions that he and his seductress would share offspring, predictions that could have been perceived as justifying an intimate relationship with Potifar’s wife.
The Midrash here reminds us how easy it is to concoct justifications for even that which is unquestionably wrong. Self-discipline is difficult in its own right, but becomes even more difficult when we entertain false rationales for why improper behavior is not truly improper. Chazal here urge us to be honest with ourselves, avoid the tendency to justify clearly inappropriate conduct, and live with a very clear sense of what is right and what is wrong.