Rabbi Yechiel Michel of Zolochow once asked why, given the emphasis Judaism places on ענוה, humility, the Torah doesn't simply command every Jew to be an ענו, a humble person. He answers, somewhat tongue in cheek, that in order to properly fulfill a Mitzvah, one must have the proper כוונה, or intent, to do so. However, anyone who declares an intention to be an ענו would automatically lack the requisite humility to fulfill such a Mitzvah.
Instead, the Torah resorts to example (see בראשית יח;כז and תהלים כב;ז) and exhortation (e.g., תהלים קמ"ט;ד). However, in all of Tanach, the only person ever actually called an ענו is Moshe Rabbeinu, at the end of this week's Parsha. Here he is described as "ענו מאד, מכל האדם אשר על פני האדמה", "exceedingly humble, more so than any other person on earth." The incident recorded here is complex and multifaceted, as are the lessons to be learned. Let's focus instead on a single perspective of those events, choosing a single set of explanations from among those offered by Chazal.
Miriam inadvertently finds out from Tzipporah that Moshe is no longer living with her. Miriam and Aharon discuss this among themselves, and conclude that Moshe acted inappropriately -- after all, they had also experienced prophecy and neither of them felt that celibacy was necessary. The Torah then describes Moshe as the epitome of humility. Hashem abruptly summons Aharon and Miriam and makes them aware of the magnitude of their error, and of their sin -- for their level of interaction with Hashem is minuscule in comparison with that of Moshe Rabbeinu. Miriam (according to some, Aharon as well) is punished with Tzoraas, leprosy. Aharon appeals to Moshe to forgive them and to pray that Miriam be healed. Moshe cries out to Hashem, who answers Moshe's request, after explaining why Miriam must wait seven days before being healed.
What, exactly, did Miriam and Aharon do wrong? The standard response is that they were guilty of Lashon Hora, slander, for which the punishment is Tzoraas. Why, then, does the Torah emphasize Moshe's humility? Would the Lashon Hora somehow be justified if Moshe were less humble? Would the magnitude of the gulf between the Kedushah, the holiness, of Moshe and that of his siblings be appreciably reduced? What is the immediate significance of Moshe's ענוה ?
Perhaps Miriam and Aharon needed to be compared with Moshe in terms of humility as well as Kedushah. Moshe's brother and sister were able to identify, emotionally and intellectually, with Tzipporah. They put themselves in her shoes, so to speak, and thus felt it necessary to come to her defense. This was admirable and correct, as far as it went. However, they were lacking in humility. They were only able to view the situation from their own perspective. Miriam and Aharon were unable to evaluate Moshe's point of view, possibly because they couldn't imagine that there was a perspective other than their own. And so they committed the sin of Lashon Hora. A truly humble person, though, is incapable of Lashon Hora.
We now have another answer to the question posed by Rabbi Yechiel Michel of Zolochow. There is a Posuk in the Torah that commands humility of every Jew: ואהבת לרעך כמוך, אני ה' -- Love your neighbor as yourself [and always be aware that] I, Hashem [require this of you].