A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
num 20:1THE DEATH OF MIRIAM. (Num. 20:1-29)
Then came the children of Israel . . . into the desert of Zin in the first month--that is, of the fortieth year (compare Num 20:22-23, with Num 33:38). In this history only the principal and most important incidents are recorded, those confined chiefly to the first or second and the last years of the journeyings in the wilderness, thence called Et-Tih. Between Num 19:22 and Num 20:1 there is a long and undescribed interval of thirty-seven years.
the people abode in Kadesh--supposed to be what is now known as Ain-el-Weibeh, three springs surrounded by palms. (See on Num 13:26). It was their second arrival after an interval of thirty-eight years (Deu 2:14). The old generation had nearly all died, and the new one encamped in it with the view of entering the promised land, not, however, as formerly on the south, but by crossing the Edomite region on the east.
Miriam died there--four months before Aaron [Num 33:38].
num 20:2there was no water for the congregation--There was at Kadesh a fountain, En-Mishpat (Gen 14:7), and at the first encampment of the Israelites there was no want of water. It was then either partially dried up by the heat of the season, or had been exhausted by the demands of so vast a multitude.
num 20:6Moses and Aaron went from the presence of the assembly--Here is a fresh ebullition of the untamed and discontented spirit of the people. The leaders fled to the precincts of the sanctuary, both as an asylum from the increasing fury of the highly excited rabble, and as their usual refuge in seasons of perplexity and danger, to implore the direction and aid of God.
num 20:8Take the rod--which had been deposited in the tabernacle (Num 17:10), the wonder-working rod by which so many miracles had been performed, sometimes called "the rod of God" (Exo 4:20), sometimes Moses' (Num 20:11) or Aaron's rod (Exo 7:12).
num 20:10[Moses] said unto them, Hear now, ye rebels; must we fetch you water out of this rock?--The conduct of the great leader on this occasion was hasty and passionate (Psa 106:33). He had been directed to speak to the rock [Num 20:8], but he smote it twice [Num 20:11] in his impetuosity, thus endangering the blossoms of the rod, and, instead of speaking to the rock, he spoke to the people in a fury.
num 20:11the congregation drank, and their beasts--Physically the water afforded the same kind of needful refreshment to both. But from a religious point of view, this, which was only a common element to the cattle, was a sacrament to the people (Co1 10:3-4) --It possessed a relative sanctity imparted to it by its divine origin and use.
num 20:12The Lord spake unto Moses and Aaron, Because ye believed me not, &c.--The act of Moses in smiting twice betrayed a doubt, not of the power, but of the will of God 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.
num 20:13This is the water of Meribah--The word "Kadesh" is added to it [Deu 32:51] to distinguish it from another Meribah (Exo 17:7).
num 20:14Moses sent messengers . . . to the king of Edom--The encampment at Kadesh was on the confines of the Edomite territory, through which the Israelites would have had an easy passage across the Arabah by Wady-el-Ghuweir, so that they could have continued their course around Moab, and approached Palestine from the east [ROBERTS]. The Edomites, being the descendants of Esau and tracing their line of descent from Abraham as their common stock, were recognized by the Israelites as brethren, and a very brotherly message was sent to them.
num 20:17we will go by the king's highway--probably Wady-el-Ghuweir [ROBERTS], through which ran one of the great lines of road, constructed for commercial caravans, as well as for the progress of armies. The engineering necessary for carrying them over marshes or mountains, and the care requisite for protecting them from the shifting sands, led to their being under the special care of the state. Hence the expression, "the king's highway," which is of great antiquity.
num 20:19if I and my cattle drink of thy water, then I will pay for it--From the scarcity of water in the warm climates of the East, the practice of levying a tax for the use of the wells is universal; and the jealousy of the natives, in guarding the collected treasures of rain, is often so great that water cannot be procured for money.
num 20:21Edom refused to give Israel passage through his border, &c.--A churlish refusal obliged them to take another route. (See on Num 21:4; Deu 2:4; and Jdg 11:18; see also Sa1 14:47; Sa2 8:14, which describe the retribution that was taken.)
num 20:22the children of Israel . . . came unto mount Hor--now Gebel Haroun, the most striking and lofty elevation in the Seir range, called emphatically "the mount" [Num 20:28]. It is conspicuous by its double top.
num 20:24Aaron shall be gathered unto his people--In accordance with his recent doom, he, attired in the high priest's costume, 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.
num 20:26strip Aaron of his garments--that is, his pontifical robes, in token of his resignation. (See Isa 22:20-25).
put them on his son--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.
num 20:28Aaron died there in the top of the mount--(See on Deu 10:6). A tomb has been erected upon or close by the spot where he was buried.
num 20:29When all the congregation saw that Aaron was dead--Moses and Eleazar were the sole witnesses of his departure (Num 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. (See on Deu 34:8).