"Listen to this, you priests! Listen, house of Israel, And give ear, house of the king! For the judgment is against you; For you have been a snare at Mizpah, And a net spread on Tabor.
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."