The revenger of blood - גאל הדם goel haddam, the redeemer of blood; the next in blood to him who was slain. See on Num 35:12 (note).

Because he should have remained in the city of his refuge until the death of the high priest,.... Nothing could give him his liberty but his death; so that though this was a merciful provision made in such cases for such persons, and was a considerable benefit and privilege, yet it carried in it some appearance of a punishment; since such a person was confined within the boundaries of one of the cities of refuge as long as the high priest lived; and this was done to make persons cautious how they were any way accessory to the death of another, though without design:

but after the death of the high priest the slayer shall return into the land of his possession; to that part of the land, and to that tribe to which he belonged, to his house and family, and to his possessions and inheritances, whatever he had, and to all the honours and privileges he before enjoyed, and under no danger from the avenger of blood henceforward: a custom somewhat like this has prevailed in some parts of Africa, as Leo Africanus (y) relates, that if a man happened to kill another, all the friends of the deceased conspired to kill him, but if they could not effect it, then the guilty person was proclaimed an exile from the city, for the whole space of seven years; and at the expiration of the whole seven years, when he returned from his exile, the chief men of the city invited him to a feast, and so he was restored to his liberty: temples, groves, altars, and statues, were common among other nations for asylums or refuges, but whole cities very rarely with the ancients; it seems there were some (z).

(y) Descriptio Africae, l. 2. p. 135, 136. (z) Vid. Marmor. Oxon. & Not. in ib. p. 25. & Rittershusium de Jure Asylorum, c. 2.

But if he thrust him suddenly without enmity, or have cast upon him any thing without laying of wait, &c.--Under the excitement of a sudden provocation, or violent passion, an injury might be inflicted issuing in death; and for a person who had thus undesignedly committed slaughter, the Levitical cities offered the benefit of full protection. Once having reached the nearest, for one or other of them was within a day's journey of all parts of the land, he was secure. But he had to "abide in it." His confinement within its walls was a wise and salutary rule, designed to show the sanctity of human blood in God's sight, as well as to protect the manslayer himself, whose presence and intercourse in society might have provoked the passions of the deceased's relatives. But the period of his release from this confinement was not until the death of the high priest. That was a season of public affliction, when private sorrows were sunk or overlooked under a sense of the national calamity, and when the death of so eminent a servant of God naturally led all to serious consideration about their own mortality. The moment, however, that the refugee broke through the restraints of his confinement and ventured beyond the precincts of the asylum, he forfeited the privilege, and, if he was discovered by his pursuer, he might be slain with impunity.