The censers of these sinners at the cost of their lives, let them make them hammered plates for a covering of the altar: for they offered them before the LORD, therefore they are hallowed: and they shall be a sign unto the children of Israel.
Read Chapter 16
George Leo Haydock
Sinners. These censers were sanctified or set apart for God's altar: 1. By the intention of those who used them, though contrary to his will; 2. by the exemplary vengeance which he exercised upon the rash pretenders to the priesthood; 3. by being a monument of their folly, and therefore placed, by God's order, upon the altar, to deter all others from imitating their conduct. Eleazar was commanded to take them up, and scatter the strange fire; that Aaron might not be defiled with touching the carcasses or ashes of the deceased, nor seem to exult in their death. (Calmet)
God was thus also pleased to manifest, that the children of Aaron, and not of the other Levites, should succeed him. (St. Augustine, q. 30.) (Worthington)