The Rambam's Fifth Principle: The reason for a mitzvah is not itself a mitzvah

Sometimes the Torah gives us the reason for a mitzvah. It may sound like a separate mitzvah, but it’s not. For example, the Torah speaks of a man who divorces his wife, who subsequently remarries. The Torah tells us that, if her second marriage dissolves, he may no longer take her back. Deuteronomy 24:4 says, “Her first husband, who sent her away, may not take her again to be his wife…” The same verse concludes, “You shall not bring sin into the land…” This may sound like a separate mitzvah, but it’s not. It’s the reason for the commandment not to remarry her.

Another example: Leviticus 19:29 prohibits immorality saying, “Do not permit your daughters to behave promiscuously,” followed by, “and do not allow the land to become lewd and full of perversion.” The latter part is the explanation for the former, not a separate injunction.

The Rambam provides several more such examples, accompanied by proofs from the Talmud and Midrash that his analysis is correct. For example, the Talmud in Zevachim 16a cites the verse, “He shall not leave the Sanctuary and he shall not cause the Sanctuary to become defiled” (Leviticus 21:12 – the referent there is the Kohein Gadol attending a funeral). The Talmud equates going out with defiling: one who goes out defiles, while one who does not go out does not defile. We see from this that “do not defile” is certainly not a separate prohibition.

Maimonides concludes that this is a principle in which some earlier compilers also erred, but counting the reasons of mitzvos separately is completely baseless. If one were to ask how a person fulfills or violates such “commandments” as not to bring sin into the land, not to fill the land with immorality and not to cause the Mishkan to become defiled (our three examples, above), there would be no answer. If these are not the reasons underlying other mitzvos, then there is no frame of reference in which to contextualize them.