And they envied He refers here very shortly to another transgression, and that, too, in such a way as to furnish both to himself and others ample grounds for deep consideration. For, as the people, in devising from time to time new modes of sinning, displayed so much cunning in their attempts to provoke God's anger, so we ought the more to be filled with fear on that account. Moreover, when he says that they envied Moses and Aaron, his meaning is, that, acting under the influence of diabolic pride, they had risen up against God, and were endeavoring to throw off the yoke which he had laid upon them; according as Moses also said, "What am I, and what is Aaron, that ye murmur against us?" (Numbers 16:11) As it was the will of God to rule the people by means of Moses and Aaron, not to submit to their rule was virtually to set themselves obstinately to resist the authority of God himself. There is therefore great importance attached to the term, envy, namely, that at the very time when God was treating the children of Israel with the utmost kindness and care, they yet were discontented with their lot, and rebelled against him. Could such madness serve any other purpose than to show, that, casting off all farther dependence upon the providence of God for their support, they aspire to rise above the very heavens? In this sense Aaron is called the saint of Jehovah, [1] in order that we might know that both he and Moses were equally identified with God; for under the person of the one, the designation is applied to both, and in this way the prophet shows that they had been Divinely invested with that authority which they were exercising. In renouncing their authority, therefore, and, to the utmost of their power, dishonoring these saints, Dathan and Abiram were rebelling not against men, but against God.

Footnotes

1 - "The saint, i.e., a man consecrated with holy oil to the office of the priesthood, and wearing on his mitre a plate inscribed, Holiness to the Lord,' (Exodus 28:36)" -- Cresswell. qdvs yhvh, holy of the Lord. Aaron is thus called, because he was separated from the whole congregation of Israel, and appointed to direct the public worship, and to offer the sacrifices. In reference to this, Moses said to Korah, The Lord will show who are His, and who is holy,' (Numbers 16:5) -- Phillips.

They envied Moses also in the camp - They were envious of him, or rebelled against him, as assuming too much authority. See Numbers 16:1-2. The reference here is rather to the "result" of that envy in producing rebellion than to the envy itself. It is true, however, that the foundation of their opposition to him "was" envy.
And Aaron the saint of the Lord - That is, as set apart to the service of the Lord; or, as employed in holy things. The reference is to his "office," not to his personal character.

They envied Moses - A reference to the case of Korah and his company.
Aaron the saint - The anointed, the high priest of the Lord.

They envied Moses also in the camp,.... That he should be generalissimo there, have the sole command of the people, and be their leader and chief magistrate. Gifts qualifying men for civil government are from the Lord, and these commonly draw the envy of others upon them; who, though they pretend patriotism and the good of their country, yet seek themselves; and would be in the places of those they envy and speak against; which was the case of Dathan and Abiram, the sons of Reuben, who thought themselves as fit, and had a better right, as being the sons of Jacob's firstborn, to command, than Moses.
And Aaron the saint of the Lord; who was not only a holy good man, but was separated from his brethren, sanctified, and put into the priest's office, and this drew upon him the envy of many of the Levites, at the head of whom was Korah, a Levite; these envied that he should be the high priest, and that this office should be restrained to his family; now the envy to each of these is ascribed to the whole body of the people, though discovered only in some, because it was not opposed by them; see Numbers 16:1.

All the congregation took part with Dathan, Korah, &c., and their accomplices (Numbers 16:41).
Aaron the saint--literally, "the holy one," as consecrated priest; not a moral attribute, but one designating his office as holy to the Lord. The rebellion was followed by a double punishment: (1) of the non-Levitical rebels, the Reubenites, Dathan and Abiram, &c. (Deuteronomy 11:6; Numbers 26:10); these were swallowed up by the earth.

The saint - So called, because he was consecrated by God for that sacred office of the priesthood, in which respect all the priests are said to be holy, Leviticus 21:6-8. Hereby he intimates, that their envy and rebellion was not only against Aaron, but against God himself.