Rashi explains that Hashem’s complaint against them stemmed from the fact that had they spoken to the rock, as they were commanded, it would have brought forth water and Hashem’s Name would have been sanctified. Klal Yisrael would have said, “Now, if this rock, which neither speaks nor hears and does not need subsistence, fulfills the word of Hashem, how much more so should we fulfill His word.” While this may be true, the words expressed in the Torah in criticizing them, “because you did not believe in Me,” are, at best, enigmatic. Moshe Rabbeinu was the greatest believer. Aharon accepted Hashem’s Divine decree against his sons with utmost faith. To say that they did not believe is a rather strong condemnation. Furthermore, how does speaking to the rock instead of hitting it, constitute a greater source of Kiddush Hashem, sanctification of Hashem’s Name? In any event, they both defy the laws of nature. What more is there to consider?
Horav Zaidel Epstein, Shlita, offers a profound exegesis, distinguishing between the two. Speaking to the rock, thus causing water to emerge from the rock, is considered a ratzon, a willing act, while causing water to run as a result of hitting the rock is an act of hechrech, compulsion, force. Both acts teach the importance of listening to the dvar Hashem, word of G-d. If we derive only that one must listen to Hashem when he is compelled, under duress, the lesson is not as compelling as learning the importance of listening to Hashem willingly. Failure to teach the complete lesson is reason enough to prevent Moshe from entering Eretz Yisrael.
We see from here the depth of din, justice, which Hashem is demanding of the righteous. For any other person, hitting the rock in order to cause water to run constitutes a sanctification of Hashem’s Name. For Moshe, it could have been a greater, more penetrating lesson – and it was not. It is a chillul Hashem for which he must answer. Moreover, we learn from this incident that a person is judged commensurate with his abilities. Even if a person has done much, if he could have done more – or better – then what he has done is not enough. Imagine, says Horav Epstein, two great Roshei Yeshiva, Torah disseminators of the highest degree, who have each successfully prepared a generation of students in Torah scholarship. If one has been granted greater talent and superior abilities to the other, however, it is quite possible that he will be taken to task for not doing more. Success is measured by what one has accomplished relative to what he could have achieved.