The establishment of the these two types of cities served as not just concepts or reminders, but actual provisions for actual people that also served to show just how precious the blood of men was to the YHWH and the essential role that priests play not only in the application of the law, but in the proclamation of grace and restoration. What God is showing Israel over and over again, even as the law is woven into their hearts and life, is that God loves those who are His, those who are under the law, under the curse, prone to wander and war, and to Redeem them and protect them through the Priest who stands between God and men.