That it might cause fury to come up to take vengeance; I have set her blood upon the top of a rock, that it should not be covered.
That it might cause fury to come up to take vengeance. God purposely let her so shamelessly pour the blood on the bare rock "that it might" the more loudly and openly cry for vengeance from on high; and that the connection between the guilt and the punishment might be the more palpable. The blood of Abel, though the ground received it, still cried to heaven for vengeance (Genesis 4:10-11); much more blood shamelessly exposed on the bare rock.
I have set her blood upon the top of a rock - she shall be paid back in kind (Matthew 7:2). She openly shed blood, and her blood shall openly be shed.