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 F25 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 F26.
The Brenton translation of the Septuagint is in the public domain.