Albert Barnes Commentary Numbers 35:16-25

"But if he smote him with an instrument of iron, so that he died, he is a murderer: the murderer shall surely be put to death. And if he smote him with a stone in the hand, whereby a man may die, and he died, he is a murderer: the murderer shall surely be put to death. Or if he smote him with a weapon of wood in the hand, whereby a man may die, and he died, he is a murderer: the murderer shall surely be put to death. The avenger of blood shall himself put the murderer to death: when he meeteth him, he shall put him to death. And if he thrust him of hatred, or hurled at him, lying in wait, so that he died, or in enmity smote him with his hand, so that he died; he that smote him shall surely be put to death; he is a murderer: the avenger of blood shall put the murderer to death, when he meeteth him. But if he thrust him suddenly without enmity, or hurled upon him anything without lying in wait, or with any stone, whereby a man may die, seeing him not, and cast it upon him, so that he died, and he was not his enemy, neither sought his harm; then the congregation shall judge between the smiter and the avenger of blood according to these ordinances; and the congregation shall deliver the manslayer out of the hand of the avenger of blood, and the congregation shall restore him to his city of refuge, whither he was fled: and he shall dwell therein until the death of the high priest, who was anointed with the holy oil." — Numbers 35:16-25 (ASV)

The meaning is: Since taking another person’s life by any means whatever is murder and exposes the murderer to the penalty of retaliation, if the deed is done in hostility, it is indeed actual murder, and the murderer is to be killed. However, if it is not done in hostility, then the congregation is to intervene to stop the avenger’s hand (Numbers 35:19).

When he meets him—provided, of course, he was outside a city of refuge (Numbers 35:24).

The case of the innocent slayer is considered here. In a doubtful case, a judicial decision would necessarily be required to determine the guilt or innocence of the person who claimed the right of asylum (Numbers 35:25).

The manslayer was safe only within the walls of his city of refuge, becoming a virtual exile from his home. The provisions made here serve to mark the gravity of the act of manslaughter, even when not premeditated; and the resulting inconveniences rightly and fairly fell upon the one who committed the deed.

Until the death of the high priest—The atoning death of the Savior cast its shadow beforehand on the statute-book of the Law and on the annals of Jewish history. The high priest—as the head and representative of the whole chosen family of sacerdotal mediators, as exclusively entrusted with some of the chief priestly functions, as the one uniquely privileged to make yearly atonement within the holy of holies, and to obtain from the mysterious Urim and Thummim special revelations of the will of God—was, preeminently, a type of Christ. Thus, the death of each successive high priest foreshadowed that death of Christ by which the captives were to be freed, and the remembrance of transgressions was to cease.