After they had set out from Kadesh, the whole congregation of Israel came to Mount Hor.
The chapter began with the funeral of Miriam, and it ends with the funeral of her brother Aaron. When death comes into a family, it often strikes double. Israel had not improved the former affliction they were under, by the death of the prophetess, and therefore, soon after, God took away their priest, to try if they would lay that to heart.
Commenting on Numbers 20:22-29
And the Lord spake unto Moses and Aaron in Mount Hor,.... When they were at the foot of that mountain, in the valley adjoining to it: by the coast of the land of Edom; which they were still upon the borders of, and were going round it, not being permitted to go through it: saying; as follows.
the 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.