Job 16:19 (ESV)

19 Even now, behold, my witness is in heaven, and he who testifies for me is on high.

Job’s blood is the earthly witness of his innocent suffering. Yet there is a higher witness, God himself, who reigns in heaven. Job had complained about God’s unjust dealings with him, and yet God remains his only hope. God is his witness, the only one from whom justice can be found.