Numbers 16:40 (BSB)

just as the LORD commanded him through Moses. This was to be a reminder to the Israelites that no outsider who is not a descendant of Aaron should approach to offer incense before the LORD, lest he become like Korah and his followers.

From Numbers 16. Also in the ESV.

Commentary on Numbers 16:40

• John Calvin (Reformed), Calvin's Commentaries on Numbers 16:40: 40. To be a memorial unto the children of Israel. This passage again confirms what I have just said, that God’s judgments, which ought to remain in full remembrance in every age, straightway escape, and are blotted out front men’s minds, unless they are provided with certain aids to meditate upon them. This, however, does not happen so much from ignorance as neglect.
• Matthew Henry (Presbyterian), Matthew Henry's Complete Commentary on Numbers 16:35-40: We must now look back to the door of the tabernacle, where we left the pretenders to the priesthood with their censers in their hands ready to offer incense; and here we find, I. Vengeance taken on them, Num 16:35.
• John Gill (Reformed Baptist), Exposition of the Old and New Testaments on Numbers 16:40: To be a memorial unto the children of Israel,.... The whole body of them; this explains what is meant by sign, Num 16:38; that it was to put or keep in mind what follows: that no stranger which is not of the seed of Aaron come near to offer incense before the Lord; not only any Gentile but any Israelite, and not any Israelite only...
• Geneva Bible Notes (Reformed), Geneva Bible Study Notes on Numbers 16:40: [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. (q) Who presumed above his calling.