Avenger of Blood

In Numbers 35, the Kinsman Redeemer (i.e., the Avenger of Blood) was required to seek out the death of the man-slayer. Why? It's not familial devotion, and it's not "righteous anger." The reason is given in vs. 33-34: to cleanse the land. Cf. Genesis 4; the ground is bloody and cries forth for vengeance.

He had to stay in a City of Refuge until the death of the High Priest. Then--and only then--he was free to live. The blood of the High Priest cleanses the land and atones for his manslaughter. Only the death of the High Priest himself can satisfy the ground's cry for vengeance.

Jesus' crucifixion was the death of the High Priest. He cleansed the land; the ground no longer cries out for our blood. Now we are free to live.