What does the plumb line mean?

Ted: God's "plumb," or the standard by which people are measured and tested, is righteousness (Isaiah 28:17). God had been merciful to Israel, over and over again, forgiving their pride, shame, and disobedience. Amos had influenced God to withhold a couple of plagues from Israel (Amos 7:1-6), but after that God would tolerate no more. It was sort of like He was "drawing a line in the sand." After that, Israel's serving other gods (which would be demonstrating a lack of righteousness) would result in the high places and sanctuaries of those other gods being destroyed and ruined; furthermore, many would die by the sword (7:9).