In introducing the Mitzvah of the Para Aduma, the Red Heifer, we read the words: ZOT CHUKAT HATORAH, “This is the law of the Torah…” (Num. 19,2) Rightfully the wording should have been ZOT CHUKAT HAPARA, “This is the law of the heifer”, since what follows is the law of preparing the Red Heifer whose ashes mixed with water were to comprise the water of purification.
The rationale for the Red Heifer is not understood and one would think that since there is no logical explanation for performing this law then we are really not duty bound to carry it through. Hence the wording is “This is the law of the Torah…” That means, this it the Torah, whether you can comprehend its meaning or not, this is the Torah and you are obligated to perform it.
Many of the Mitzvot in the Torah are logical and their motive is understandable. What the Torah wants us to realize is that when we perform a Mitzvah it should be because Hashem commanded us and not because it makes sense to do so.
If one asks why is it so important to perform the Mitzvah because we were commanded and not because we understand its value, the answer is simple. If we act properly because it is logical, we can always find a justification why in a specific case we do not have to perform it due to particular circumstances. One can always rationalize his actions without much effort.