Matthew Henry on Numbers 16:35-40

A fire went out from the Lord, and consumed the two hundred and fifty men that offered incense, while Aaron, who stood with them, was preserved alive. God is jealous of the honour of his own institutions, and will not have them invaded. The sacrifice of the wicked is an abomination to the Lord. The censers are devoted, and, as all devoted things, must be made serviceable to the glory of God. This covering of the altar would remind the children of Israel of this event, that others might hear and fear, and do no more presumptuously. They brought destruction on themselves both in body and soul. Thus all who break the law and neglect the gospel choose and love death.