And when all the congregation saw that Aaron was dead, they mourned for Aaron thirty days, even all the house of Israel.

Wesley's Notes

20:29 Saw - Understood by the relation of Moses and Eleazar, and by other signs. Thirty days - The time of publick and solemn mourning for great persons.

Jamieson-Fausset-Brown Bible Commentary

29. When all the congregation saw that Aaron was dead-Moses and Eleazar were the sole witnesses of his departure (Nu 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 (Le 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 [85]De 34:8).

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?