Numbers 35:25 (NKJV)
So the congregation shall deliver the manslayer from the hand of the avenger of blood, and the congregation shall return him to the city of refuge where he had fled, and he shall remain there until the death of the high priest who was anointed with the holy oil.
God instituted a strange law that the Israelites setup six cities to which a person could flee to safety if he had committed an accidental murder. The kinsman of the person murdered would be the Avenger of Blood, but he could not carry out his vengeance while the person was in the City of Refuge. Only if the person left that city could the avenger take his vengeance. The strange thing is that when the high priest of that city died, the person who committed the manslaughter would be free to return to his home without consequence.
Why did God put this in the Bible? We can see elements of this in our own judicial system: protection by the courts, trials with defense and prosecuting attorneys, etc.
The Cities of Refuge have a deep theological meaning. We are all guilty of the death of Christ because of our sin. But we were born sinners and in that sense we could not avoid our guilt. But what is our refuge? Jesus is our City of Refuge and being in him, we are saved from the Avenger of Blood, the judgment of God. Jesus is the great high priest who died for us. His death represents the cancellation of sin for those who have fled to Him as their refuge.
One final thing: the six Cities of Refuge were to be conveniently located so that they would be easily accessible from anywhere in the land. So too, Jesus is easily accessible, so that anyone may come to him from anywhere at anytime.
Romans 8:1a (NKJV)
There is therefore now no condemnation to those who are in Christ Jesus