G‑d told Moshe to conduct a test that would demonstrate the error of Korach and his fellow rebels against Moshe. Offering up incense is part of the Mishkan service that was allowed to be performed only by the Kohanim and only at specific times.

The Jewish People had previously witnessed how Aaron’s sons, Nadav and Avihu, had died on account of having offered up an unauthorized incense offering. Now, G‑d had told Moshe to instruct Korach and his band of rebels to offer up incense as Aaron would. Whoever’s incense is not accepted by G‑d would die immediately. As the Torah states “Let each man take his censer and place incense in it, and let each man present his censer before G‑d.” (Bamidbar 16)

Although Korach and his company of mutineers knew that unauthorized use of the incense would cause their deaths, they still took up the challenge. They wished to experience the lofty and ecstatic service of the Kohen Gadol even if it would cost them their lives.

In this sense, their motivation was holy. We can learn from their example, by aspiring to the most uplifting spiritual experiences to come closer to G‑d.

Thus, the Lubavitcher Rebbe asks, so what was the sin of Korach and his followers? The Rebbe answers that their sin was the absurdity and the paradox of going against G‑d’s will in order to get close to Him!

The message for us is that in Judaism, even if your motives are holy, you cannot make up your own rules, but must go only by the Good Book. Thus, in a sense, you could say that Korach and his followers were the first to attempt to make Judaism conform to THEIR beliefs rather than to G‑d’s commands.