Or HaChaim on Numbers 17:11/אור החיים על במדבר י״ז:י״א

1 קח את המחתה, "take the censer, etc." Inasmuch as the people had claimed that the reason the 250 men had died was due to Moses having challenged them to offer the deadly incense, Moses now wanted to demonstrate that incense is far from deadly; on the contrary, this very "deadly" incense would now save the people's lives. The reason the incense had appeared to be "deadly" was because the wrong people had offered it at the wrong time and at the wrong place. Our sages in Shabbat 89 claim that Moses had learned the life-saving property of the incense offering from the angel of death himself when he had been on Mount Sinai waiting to receive the Tablets and the Torah.