“For her blood is in the midst of her. She set it on the bare rock. She did not pour it on the ground to cover it with dust. That it might cause fury to come up to take vengeance I have set her blood on the bare rock that it should not be covered.”
The people of Jerusalem were totally unashamed of their sins. The blood they had spilled was not hidden but displayed for all to see, both the blood of violence and the blood of child sacrifice. Like the blood of Abel it cried to God for vengeance (Genesis 4:10 compare Job 16:18). Had it been blood which was rightly shed they would have covered it with dust (Leviticus 17:13), although in fact had they done so it would not have remained covered, for it was unrighteously shed and would still not have been hidden (Isaiah 26:21).
Ezekiel's priestly way of thinking comes out here. The blood displayed on the rock was against all the tenets of the Law, it was wrongly dealt with and therefore brought further defilement, which brought out the guiltiness of those involved. It doubly proved that they were not righteous men, but were men of blood.
With a sudden turn in thought we then learn that this was Yahweh's doing. He would not let the blood be covered up, for it was His purpose to exact vengeance for it.
But it was not enough just to deal with the inhabitants, Jerusalem itself must be destroyed, all the filth along with the flesh.