Death of Aaron

[Num. 20:12] And the LORD spake unto Moses and Aaron, Because ye believed me not, to sanctify me in the eyes of the children of Israel, therefore ye shall not bring this congregation into the land which I have given them.
[24] Aaron shall be gathered unto his people: for he shall not enter into the land which I have given unto the children of Israel, because ye rebelled against my word at the water of Meribah.
The act of Moses in smiting twice betrayed a doubt, not of the power, but of the will of G-d to gratify such a rebellious people, and his exclamation seems to have emanated from a spirit of incredulity akin to Sarai's (Gen. 18:13). These circumstances indicate the influence of unbelief, and there might have been others unrecorded which led to so severe a chastisement. And yet they did not doubt of the power of G-d, but of his will, whether he would gratify these rebels with this farther miracle, after so many of the like kind.
To sanctify Me is to give the glory of My power in doing this miracle, and of My truth in punctually fulfilling My promise, and of My goodness in doing it notwithstanding the peoples perverseness.
In the eyes of Israel this made their sin scandalous to the Israelites, who of themselves were too prone to infidelity; to prevent the contagion, G-d leaves a monument of his displeasure upon them, and inflicts a punishment as public as their sin.
These two dear brothers must part! Aaron must die first: but Moses is not likely to be long after him. So that it is only for a while, a little while, that they are separated.]
In accordance with his recent doom, he, attired in the high priest's robes, was commanded to ascend that mountain and die. But although the time of his death was hastened by the divine displeasure as a punishment for his sins, the manner of his death was arranged in tenderness of love, and to do him honor at the close of his earthly service. His ascent of the mount was to afford him a last look of the camp and a distant prospect of the Promised Land. The simple narrative of the solemn and impressive scene implies, though it does not describe, the pious resignation, settled faith, and inward peace of the aged pontiff.
Strip Aaron of his garments that is, his priestly robes, in token of his resignation. (See Isaiah 22:20-25). Put them on his son - Eleazar as the inauguration into his high office. Having been formerly anointed with the sacred oil, that ceremony was not repeated, or, as some think, it was done on his return to the camp.
Ye – Moses, because they rebelled, this was one but not the only reason. G-d, would not have Moses and Aaron to carry the people into Canaan, for this reason also, to signify the insufficiency of the Mosaical law and Aaronical priesthood to make them perfectly happy, and the necessity of a better, and to keep the Israelites from resting in them, so as to be taken off from their expectation of Messiah.
Aaron died there in the top of the A tomb has been erected upon or close by the spot where he was buried. He died in Mosera (Deut. 10:6). Mosera was the general name of the place where that station was, and mount Hor a particular place in it. Presently after he was stripped of his priestly garments, he laid him down and died. A good man would desire, if it were the will of G-d, not to outlive his usefulness. Why should we covet to continue any longer in this world, than while we may do G-d and our generation some service? Moses death ended the years of wandering.
Moses and Eleazar were the sole witnesses of his departure (20:28). According to the established law, the new high priest could not have been present at the funeral of his father without contracting ceremonial defilement (Lev. 21:11). But that law was dispensed with in the extraordinary circumstances. The people learned the event not only from the recital of the two witnesses, but from their visible signs of grief and change; and this event betokened the imperfection of the Levitical priesthood (Heb. 7:12).
They mourned for Aaron thirty days - the usual period of public and solemn mourning.