We know that on Pesach there is a prohibition of bal yeira’eh u’bal yimatzei—one may not possess chametz. In addition, there is a positive mitzvah of tashbisu, to destroy the chametz.

The question raised is: what happens if a person eats chametz on Pesach? On the one hand, he is clearly violating a Torah prohibition by eating chametz. However, at the same time, he is removing and destroying the chametz through the act of eating it. Does this mean that he has, in some sense, fulfilled the mitzvah of tashbisu?

The Rebbe brings that there is a dispute among the authorities. The sefer Teshuvah Me’ahavah holds that in fact, one has fulfilled the mitzvah of destroying chametz, since the chametz has been eliminated. This is in contrast to other opinions that maintain that one does not fulfill the mitzvah in such a manner.

The Rebbe further notes that from several Rishonim it appears that even though eating chametz is strictly prohibited, it may still be considered a form of removal. In other words, the act is unquestionably forbidden, yet the result—namely, that the chametz is no longer in existence—may technically align with the concept of tashbisu.

Nevertheless, this does not in any way justify the act. The person is committing a serious prohibition, and the possible fulfillment of tashbisu does not mitigate or permit the violation.

Summary
While eating chametz on Pesach is a clear prohibition, there is a discussion whether it technically fulfills the mitzvah of destroying chametz. Some opinions say yes, since the chametz is removed, while others disagree—but all agree the act remains strictly forbidden.