Tell the people of Isra’el, ‘Select the cities of refuge about which I spoke to you through Moshe; so that anyone who kills someone by mistake and unknowingly may escape there; they will serve as refuges for you from the next-of-kin avenger.
The next-of-kin avenger, or the blood avenger is a neat concept. The Almighty has a life of bounty and good prepared for Israel, but that doesn’t mean it will be free from accident or mishap. As the text explains here and elsewhere, sometimes people die accidentally. When that death comes through the hand of someone without their intent, it still hurts the dead person’s family as much as any death. Remember that Abel’s blood cried out from the ground which swallowed it after Kane murdered him. When someone commits a murder the Torah states that the Land will be satisfied by the murderer’s death. There is nuance and detail I am omitting here, but only to focus on a different idea, so don’t assume ancient Israel was a blood-soaked feud country. There is a primal urge to payback someone for what they did. Kane shed Abel’s blood, so someone should shed his, that will make it better right? It reminds me of my children: one of them hurts the other, so the sibling strikes back. Once they have exchanged hits, they don’t calmly retreat and rethink their lives. They dig in and their defenses go up. Everyone knows that the best defense is a good offense, so they keep escalating and it can become a full-on fight. Those same types of feelings persist in a situation like this, where death comes without intent. The avenger wants to satisfy the death of their loved one with the death of the one who caused it. It’s very natural. But our Heavenly Father desires more. He has Israel set up the cities of refuge as a sanctuary where the avenger could not enter for the purpose of killing the inadvertent killer. The killer had to make it to the city of refuge though to gain this protection. If the avenger caught them before this, they were held guiltless for killing the killer. As I understand it, the family of the refugee would not be able to avenge their blood against the original avenger and be held blameless. That’s a neat system; very well thought out and quite merciful. Life is complicated and thank Heaven, the Almighty is merciful and makes provisions for our frailty.