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.