Numbers 16:5, 40

Then he said to Korah and all his followers: “Tomorrow morning the LORD will show who belongs to him. He will bring the one who is holy near to him; he will bring to himself the person he chooses.

as the LORD had commanded him through Moses. These sheets were to remind the Israelites that only descendants of Aaron should burn incense before the LORD. Anyone else would die like Korah and his followers.