And the Lord spoke to Moses, saying, “Speak to the people of Israel and say to them, When you cross the Jordan into the land of Canaan, then you shall select cities to be cities of refuge for you, that the manslayer who kills any person without intent may flee there. The cities shall be for you a refuge from the avenger, that the manslayer may not die until he stands before the congregation for judgment. And the cities that you give shall be your six cities of refuge. You shall give three cities beyond the Jordan, and three cities in the land of Canaan, to be cities of refuge. These six cities shall be for refuge for the people of Israel, and for the stranger and for the sojourner among them, that anyone who kills any person without intent may flee there. Numbers 35:9-15, ESV.
Why does God demand that Israel set up cities of refuge in the Promised Land? Gerard Van Groningen offers a threefold explanation:
First, the holiness of the Lord is to be maintained. The shedding of blood defiles the land. The Lord dwells among his people and will not tolerate willful defilement of his holiness. Second, mercy has to be shown. Not every person who kills another does so intentionally. Such a person has to have a means to escape the avenger of blood by fleeing to the nearest city of refuge and remaining in it until the death of the high priest in office at the time of the killing. Third, justice has to be carried out for the unintentional as well as the intentional murder. All human life is precious in the sight of the Lord. Anyone who destroys it has to forfeit his life at the hand of a family’s avenger of blood or give up a great measure of freedom by remaining in the city. If a murderer escapes to a city of refuge, and two or more witnesses testify to the intentional killing, by whatever means, the avenger has to destroy the murderer. Justice also requires that neither the unintentional nor intentional murder can be ransomed. Thus the rich and poor, as well as the native and stranger are dealt with impartially.
The city of refuge is a place where the holiness, mercy, and justice of the Lord meet. These cities provide a prophetic glimpse of Jesus on the cross. As Jesus, the sinless Lamb of God, died in our place, a Holy God executed His justice on Him so that He might show mercy to us. That mercy is ours if we will but run in faith to His Son.
I pray that you have experienced that mercy. If not, I pray that you will trust in Jesus and find refuge today. To learn more, see http://www.ttownbaptist.org/how-can-i-be-saved.html.
 Gerard Van Groningen, “Numbers,” in Evangelical Commentary on the Bible, vol. 3, Baker Reference Library (Grand Rapids, MI: Baker Book House, 1995), 105.