Then you shall appoint cities to be cities of refuge for you, that the manslayer who kills any person accidentally may flee there.
Numbers 35:11

God’s law about cities of refuge in ancient Israel were God’s answer regarding the difference between murder and accidentally taking another person’s life. It not only defined the difference, but it made provision for the “manslayer” (the person guilty of involuntary manslaughter) to escape execution, while still maintaining the sanctity of human life.

Simply, if a person accidentally killed someone, to escape the execution at the hands of the “avenger of blood,” he would flee to the city of refuge for protection. The manslayer would have to remain in the city of refuge until the death of the current high priest, after which he could venture out. If the avenger of blood did anything to the manslayer after that, the avenger of blood would be guilty of murder. What gospel application is in this law?

While execution for murder was averted, there was still a burden to bear for having taken a life. This is important because human life is precious, as we are created in the image of God. This reminds us that doing harm, even unintentionally, is still harmful.
Christ is pictured in these cities, since it is to Him that we flee for protection from the consequences of wrongdoing, whether done intentionally or not.
That the manslayer was free upon the death of the high priest, we are free from all condemnation as we (a) flee to Christ, and (b) because Jesus, our Great High Priest, did die and has even risen from the dead to give us new and abundant life, even though we have sinned.