And Moses did as the LORD commanded: and they went up into mount Hor in the sight of all the congregation.

Wesley's Notes

20:27 In the sight of all the congregation - That their hearts might be more affected with their loss of so great a pillar, and that they all might be witnesses of the translation of the priesthood from Aaron to Eleazar.

Matthew Henry's Concise Commentary

20:22-29 God bids Aaron prepare to die. There is something of displeasure in these orders. Aaron must not enter Canaan, because he had failed in his duty at the waters of strife. There is much of mercy in them. Aaron, though he dies for his transgression, dies with ease, and in honour. He is gathered to his people, as one who dies in the arms of Divine grace. There is much significancy in these orders. Aaron must not enter Canaan, to show that the Levitical priesthood could make nothing perfect; that must be done by bringing in a better hope. Aaron submits, and dies in the method and manner appointed; and, for aught that appears, with as much cheerfulness as if he had been going to bed. It was a great satisfaction to Aaron to see his son, who was dear to him, preferred; and his office preserved and secured: especially, to see in this a figure of Christ's everlasting priesthood. A good man would desire, if it were the will of God, not to outlive his usefulness. Why should we covet to continue any longer in this world, than while we may do some service in it for God and our generation?