Korah accused Moses of being haughty and arrogant by telling him, “Why do you elevate yourself above the congregation of G-d that you lord over us, and wish to increase your dominance!”
However, the Torah has already described how Moses resisted accepting the position of leadership and testified that Moses was the humblest of all men upon the earth. How absurd that Korah and his assembly should accuse Moses of vanity and of making himself superior to others!
This is precisely the point that the Torah teaches us. When a person becomes involved in a personal dispute, he may lose all sense of logic and strike out indiscriminately, making the most absurd arguments and ironically many of his accusations can be found true about the accuser himself! While observers can see how this person makes an absolute fool of himself, the person is so blinded, that he may make the most ridiculous accusations.
This may well be the meaning of the verse when Moses replied to Korah, “Listen now, tribe of Levi!” Why did Moses reference the entire tribe who were not involved with the rebellion? Because, as objective observers, they would be able to attest to the absurdity of Korah’s claim.