Amo 7:7 Thus he shewed me: and, behold, the Lord stood upon a wall made by a plumbline, with a plumbline in his hand.
Amo 7:8 And the LORD said unto me, Amos, what seest thou? And I said, A plumbline. Then said the Lord, Behold, I will set a plumbline in the midst of my people Israel: I will not again pass by them any more:
A plumb line is a straight and true line by suspending a pointed weight on a string. The plumb line is a straight line and by it a wall is made straight or is seen as not truly being straight. The law of gravity keeps it perfectly straight. God would judge Israel with a perfect law, no longer would he pass by and ignore their sins. Judgement time had come.
Paul spoke of rightly dividing the word of God. I see this as a plumb line in the spiritual. We can discern the truth by correctly interpreting scriptures. The scriptures interpret scriptures. Read them, know them and then you will see truth from error.
2Ti 2:15 Study to shew thyself approved unto God, a workman that needeth not to be ashamed, rightly dividing the word of truth.
The truth of God is backed up by the authority and power of God as creator and judge. He will punish the transgressor and through faith in the Lord Jesus Christ he gives grace. When a politician makes a line, then it means that anyone stepping over it would be subject to the power that he has behind him. The big difference is that God is not a liar, he means what he says and he keeps his word. When all is said and done, God's word remains true, the plumb line of his truth and will.