Numbers 16:40

to be a reminder to the people of Israel , so that no outsider , who is not of the descendants of Aaron , should draw near to burn incense before the Lord , lest he become like Korah and his company —as the Lord said to him through Moses .

as the Lord directed him through Moses. This was to remind the Israelites that no one except a descendant of Aaron should come to burn incense before the Lord, or he would become like Korah and his followers.

To be a memorial unto the children of Israel, that no stranger, which is not of the seed of Aaron, come near to offer incense before the Lord; that he be not as Korah, and as his company : as the Lord said to him by the hand of Moses.