4 This is the guideline for the murderer who flees there to take refuge: He has to have killed his neighbor without premeditation and with no history of bad blood between them. 5 For instance, a man goes with his neighbor into the woods to cut a tree; he swings the ax, the head slips off the handle and hits his neighbor, killing him. He may then flee to one of these cities and save his life. 6 If the city is too far away, the avenger of blood racing in hot-blooded pursuit might catch him since it's such a long distance, and kill him even though he didn't deserve it. It wasn't his fault. There was no history of hatred between them. 7 Therefore I command you: Set aside the three cities for yourselves. 8 When God, your God, enlarges your land, extending its borders as he solemnly promised your ancestors, by giving you the whole land he promised them 9 because you are diligently living the way I'm commanding you today, namely, to love God, your God, and do what he tells you all your life; and when that happens, then add three more to these three cities 10 so that there is no chance of innocent blood being spilled in your land. God, your God, is giving you this land as an inheritance - you don't want to pollute it with innocent blood and bring bloodguilt upon yourselves.
Matthew Henry's Commentary on Deuteronomy 19:4-10
Commentary on Deuteronomy 19:1-13
(Read Deuteronomy 19:1-13)
Here is the law settled between the blood of the murdered, and the blood of the murderer; provision is made, that the cities of refuge should be a protection, so that a man should not die for that as a crime, which was not his willing act. In Christ, the Lord our Righteousness, refuge is provided for those who by faith flee unto him. But there is no refuge in Jesus Christ for presumptuous sinners, who go on still in their trespasses. Those who flee to Christ from their sins, shall be safe in him, but not those who expect to be sheltered by him in their sins.