When Ephraim saw his sickness, And Judah his wound, Then Ephraim went to Assyria, And sent to king Jareb: But he is not able to heal you, Neither will he cure you of your wound.
When they offer their sacrifices unto the gods in the Northern Kingdom they would do it with great flare. Again, trying to make a big deal out of it so all of the people would be in awe. So that is what is meant by "profound to make slaughter."