But if the slayer shall at any time come without the border of the city of his refuge,.... Which seems to be the three thousand cubits assigned to every city of the Levites, and so to the cities of refuge; and which, according to the Jewish writers, were a refuge, as the city itself; and it is said (x),"he, that kills a man there, is killed for him, but though the border is a refuge, the slayer does not dwell in it, as it is said. Numbers 35:25, "he shall abide in it", but not in its borders:"
whither he was fled; on account of manslaughter.
(x) Maimon. Hilchot Rotzeach, c. 8. sect. 11. Misn. Maccot, c. 2. sect. 7.

If he left the city of refuge before this, and the avenger of blood got hold of him, and slew him outside the borders (precincts) of the city, it was not to be reckoned to him as blood (דּם לו אין, like דּמים לו אין, Exodus 22:1). But after the death of the high priest he might return "into the land of his possession," i.e., his hereditary possession (cf. Leviticus 27:22), sc., without the avenger of blood being allowed to pursue him any longer.
In these regulations "all the rigour of the divine justice is manifested in the most beautiful concord with His compassionate mercy. Through the destruction of life, even when not wilful, human blood had been shed, and demanded expiation. Yet this expiation did not consist in the death of the offender himself, because he had not sinned wilfully." Hence an asylum was provided for him in the free city, to which he might escape, and where he would lie concealed. This sojourn in the free city was not to be regarded as banishment, although separation from house, home, and family was certainly a punishment; but it was a concealment under "the protection of the mercy of God, which opened places of escape in the cities of refuge from the carnal ardour of the avenger of blood, where the slayer remained concealed until his sin was expiated by the death of the high priest." For the fact, that the death of the high priest was hereby regarded as expiatory, as many of the Rabbins, fathers, and earlier commentators maintain (see my Comm. on Joshua, p. 448), is unmistakeably evident from the addition of the clause, "who has been anointed with the holy oil," which would appear unmeaning and superfluous on any other view. This clause points to the inward connection between the return of the slayer and the death of the high priest. "The anointing with the holy oil was a symbol of the communication of the Holy Ghost, by which the high priest was empowered to act as mediator and representative of the nation before God, so that he alone could carry out the yearly and general expiation for the whole nation, on the great day of atonement. But as his life and work acquired a representative signification through this anointing with the Holy Ghost, his death might also be regarded as a death for the sins of the people, by virtue of the Holy Ghost imparted to him, through which the unintentional manslayer received the benefits of the propitiation for his sin before God, so that he could return cleansed to his native town, without further exposure to the vengeance of the avenger of blood" (Comm. on Joshua, p. 448). But inasmuch as, according to this view, the death of the high priest had the same result in a certain sense, in relation to his time of office, as his function on the day of atonement had had every year, "the death of the earthly high priest became thereby a type of that of the heavenly One, who, through the eternal (holy) Spirit, offered Himself without spot to God, that we might be redeemed from our transgressions, and receive the promised eternal inheritance (Hebrews 9:14-15). Just as the blood of Christ wrought out eternal redemption, only because through the eternal Spirit He offered Himself without spot to God, so the death of the high priest of the Old Testament secured the complete deliverance of the manslayer form his sin, only because he had been anointed with the holy oil, the symbol of the Holy Ghost."

He shall abide in it - Be confined to it, partly to shew the hatefulness of murder in God's account by so severe a punishment, inflicted upon the very appearance of it, and partly for the security of the man - slayer, lest the presence of such a person, and his conversation among the kindred of the deceased, might occasion reproach and blood - shed. The death of the high - priest - Perhaps to shew that the death of Christ (the true High - priest, whom the others represented) is the only means whereby sins are pardoned and sinners set at liberty.