Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
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: KJV
{And the Lord said to me, What seest thou, Amos? And I said, A trowel of a mason. And the Lord
said, Lo! I shall put a trowel in the middle of my people Israel; I shall no more put to, for to over-lead it;} Wycliffe's Bible
I will set a plumbline - I will visit them by justice without any mixture of mercy.