Charles Ellicott Commentary Leviticus 10:3

"Then Moses said unto Aaron, This is it that Jehovah spake, saying, I will be sanctified in them that come nigh me, and before all the people I will be glorified. And Aaron held his peace." — Leviticus 10:3 (ASV)

Then Moses said ... This is what the Lord spoke. —Here we have another instance of a reference to a well-known Divine communication made through Moses, which has not been previously recorded in the Pentateuch. Moses cites this declaration to explain to the bereaved father the judgment of God.

I will be sanctified in them that come near me.—Better. I will sanctify myself in them that come near to me. God had sanctified to Himself Aaron and his sons by the holy unction (Leviticus 8:12), so that they might sanctify Him in the strict performance of their sacred duties as the mediators between God and man. Having failed to do this, God sanctified Himself in them by the awful punishment inflicted upon them for their transgression. (Ezekiel 38:16; Ezekiel 38:23.) The phrase, “that come near to God,” is a frequent designation for the priest (Exodus 19:22; Numbers 16:5; Ezekiel 42:13; Ezekiel 43:19).

And before all the people I will be glorified. —Better, and I will glorify myself before all the people. By this judgment God vindicated His law, showing that it cannot be violated with impunity, and thus glorified Himself as the Holy One of Israel.

And Aaron held his peace. —He silently submitted to the righteous judgment which bereft him of his two sons. So the Psalmist, I was dumb, I opened not my mouth; because thou didst it (Psalms 39:9).