In verse 17, the plumb line is defined as justice and righteousness. We have seen that already in our word "upright," a synonym of "vertical." What is upright is righteous, and God will judge according to that standard. He will set us up so that we can see—and He can see—how close we are adhering to godly judgment and right doing. He and we will see how much we are living by the standard.
He writes, ". . . the hail will sweep away the refuge of lies, and the waters will overflow the hiding place." The process of this judgment will sweep away 1) the deceptions that we have allowed ourselves to believe and 2) the hidden, secret sins that we have allowed to continue. We will not be able to hide from the lies and the sins that we have ignored for so long.
The plumb line is nothing to sneeze at. God is serious. When He holds the plumb line next to His people, He is deadly serious, "eternal life and death" serious—especially to those who are converted. We had better measure up.
Richard T. Ritenbaugh
The Two Witnesses (Part 5)