What did Yosef want to emphasize with the additional and seemingly redundant phrase, “You have done evil in so doing”? Horav Shlomo Harkavi Z”l. cites the Chovas Halevovos, who distinguishes between two obligatory approaches to serving Hashem. One orientation is simply that the Torah implores it. It is Hashem’s command that one performs mitzvos and avoids transgression. Hashem also demands of us that every action we do, every undertaking in which we involve ourselves, be consistent with “sechel ha’yashar,” common sense. One who acts in an irrational manner is truly reprehensible.
When one is involved in a criminal act, such as stealing, some form of “justification” is possible. His financial situation may have reached a point that he could no longer endure. His yetzer hora, evil inclination, was able to sway him towards theft. If one were to steal an article, cognizant that he would be immediately apprehended, he would be viewed as foolish. He wouldn’t simply be a thief, he would be an imbecile! Yosef told his brothers, “How could you add foolishness to your act of thievery? Do you not know that I use this cup for divining, and your act of stealing would immediately be uncovered?” Yosef rebuked them for the initial act of stealing, as well as for their failure to apply common sense.
This idea serves as a piercing condemnation regarding every aveirah, sin, we transgress. Are we so foolish to think that Hashem will not “find out” and punish us? Does anything elude Him? Likewise, it behooves us to use common sense and simple logic even in every good deed and mitzvah we perform. Even the most positive action, if performed without “sechel,” can quickly be transformed into an ugly aveirah.