a builder's plumb line: a cord with a weight on the end, hung against a wall to test whether it is true.
This word names a tool, not an idea. It is a cord with a weight tied to one end, the thing a builder hangs against a wall to find out whether the wall stands true. Its Hebrew name is built on the everyday verb for weighing, the same word used for weighing out silver, and the same family that gives the shekel its name. A weighted line is literally a "weighing thing": you hang the weight, gravity pulls the cord straight, and the cord tells you the truth about the wall.
It appears in only two verses, and in both of them God is the one holding the tool. Both times it is paired with the measuring cord (קָו), the flat line a builder stretches out to lay a course of stone. Together the two make up a surveyor's basic kit, so naming them side by side is a way of saying that the whole job of measuring is being done.
- In 2 Kings 21:13 God stretches over Jerusalem the same measuring line he once used on Samaria and the same weighted tool he used on the house of Ahab, and the measuring is done in order to pull the city down.
- In Isaiah 28:17 God makes justice the line and righteousness the weighted tool, so that his own character becomes the standard Jerusalem is tested against, and the shelter of lies does not survive the inspection.
The force of the picture is that one set of instruments does both jobs. Kings and gods across the ancient world were shown stretching out a cord to lay out a temple, and the prophets take that familiar scene and turn it around, so the tools of founding a city become the tools of condemning one. Nothing about the plumb line changes between the two verses. What changes is the wall.
Disputed
Whether מִשְׁקֶלֶת names a plumb line, which tests verticality, or a mason's level, which tests horizontality.
- majorityA plumb line or plummet: a weight suspended on a cord to test whether a wall is vertical. This is favoured by the parallelism, since קָו is already the horizontal measuring cord and the pair reads as complementary rather than synonymous, and it is the rendering of most modern English versions.; DCH (Clines), Dictionary of Classical Hebrew, s.v. מִשְׁקֶלֶת; Joseph Blenkinsopp, Isaiah 1-39 (Anchor Yale Bible 19, 2000), on Isaiah 28:17; J. J. M. Roberts, First Isaiah (Hermeneia, 2015), on Isaiah 28:17
- minorityA levelling instrument: a mason's set-level that tests horizontal accuracy. This weights the etymology, since the noun means literally a weight-tool, and ancient levels worked by a plumb bob hanging from the apex of a frame.; BDB (Brown-Driver-Briggs), s.v. מִשְׁקֶלֶת; Gesenius, Hebräisches und Aramäisches Handwörterbuch über das Alte Testament, 18th ed. (Donner and Rüterswörden), s.v. מִשְׁקֶלֶת ("Setzwaage, Bleiwaage"); Hans Wildberger, Jesaja 28-39 (Biblischer Kommentar Altes Testament X/3, 1982), on Isaiah 28:17
- minorityThe word covers the weight-based builder's instrument generally, without specifying which axis it tests, since a single suspended-weight mechanism served both functions in antiquity.; HALOT (Koehler-Baumgartner), s.v. מִשְׁקֶלֶת ("level, plumb-line"); NIDOTTE, s.v. שׁקל