The Ralbag in his lessons on this Torah portion, lesson 16, learns from the pasuk that it is not right for one who is giving rebuke to tell over something which would make it possible for those being rebuked not to accept the message. For this reason, Moshe did not want to reveal the place about which he was rebuking the Jews, that as a result of what happened at Mei Merivah (which literally means the waters of strife) Aharon died and death was decreed upon Moshe himself. This is because the sin had been forgotten and they could have said there is no point to guard oneself from sin because they (Moshe and Aharon) died without sin, with all there greatness in stature. For this reason as well, Moshe did not want to mention the incident with Korach, because of how great his stature was in their eyes; in order that they wouldn’t be able to have any room to dodge his rebuke. (Click here for Hebrew text.)
Why couldn’t Moshe, with all his expertise, explain the problem in such a way that the Jewish People could learn the proper lesson? Also, weren’t Aharon and Moshe punished for not instilling a high enough level of faith in Hashem by hitting the rock twice instead of also speaking to it (Bamidbar 20:12, 13)?
It would seem though, from the Ralbag, that the Children of Israel were held accountable for getting Aharon and Moshe into this position because they should not have started the fight to begin with. However, when rebuking them about the matter, Moshe felt it was not useful to mention it outright, because they had forgotten that they were the ultimate cause of Aharon and Moshe’s deaths, and there would be no point in reminding them of what happened, because in their minds nothing wrong was done either by them or by Moshe and Aharon. By explicitly reminding them about Mei Meriva, not only would they not learn their lesson but it would in fact be counterproductive, and they would find an excuse to sin because everyone dies, even great leaders like Moshe and Aharon who never sinned.
We see from here that Moshe and Aharon were so great that the generation wandering in the desert viewed them as having done nothing wrong, which means the mistake Moshe and Aharon did by the hitting of the rock must have been so insignificant and so minute that it was not even a blip on the radar screen of the Jewish people. And for that reason, they would mistakenly think that people die for no reason and that there is no point in avoiding sin.
What is even worse, the Ralbag points out, is that Moshe did not even bother mentioning Korach’s revolt, which seemed to have been an outright attack on Moshe and Aharon’s leadership. But upon further reflection, it would seem that in the eyes of the generation of the Jews in the desert Korach might not have been such a bad guy; albeit he and his family were swallowed alive by the earth and he was burnt up by a heavenly fire, but that must be taken into perspective. Korach was third in command behind Moshe and Aharon. He must have been a pretty righteous individual, at least in the eyes of the Jewish people, in order to gain such high stature. We know Korach argued with Moshe in Jewish law about putting tzitzis on curtains, for example, and he might have had some leadership argument – but, in all, he still seemed like quite an amazing person. Imagine two great sages from the previous generation like Rav Moshe Feinstein and Rav Aharon Kotler arguing with each other. No one would suspects that they were evil people (and they weren’t). But deep down inside, because Korach’s argument stemmed from jealousy, Hashem, who knows what is in the depths of a person’s heart, punished Korach as severely as he did, which he deserved. But it is possible that in the Jewish people’s view he might have done something wrong but have been judged according to the high level he was on – but that does not mean that they, on their lower spiritual level, could possibly learn anything from this incident. Therefore, since he was on such a different playing field, Moshe did not bother mentioning Korach in his rebuke to the Jewish people.
When teaching the important lesson of avoiding argumentation, which was the lesson of Mei Meriva and Korach, Moshe left them out because he felt mentioning them would only make things worse, because the Jewish people in the desert viewed Aharon and Moshe as perfect, and had forgotten what they did wrong. Indeed, Korach, even if he had done something wrong, it was so infinitesimal in their eyes, as they knew that the more righteous you are the more strict Hashem judges you. Therefore, even from the rebellion of Korach there would not have been a significant lesson that could have been learnt by the Jewish people.
At the very least the lesson we should take from here is to appreciate the greatness of the earlier generations. It is unfathomable!