The general meaning is plain, but the exact force of the metaphor used is not so clear. If the “line” and the “plummet” be “symbols of rule” or law, the meaning will be - “I will apply exactly the same measure and rule to Jerusalem as to Samaria - I will treat both alike with strict and even justice.”
Related Commentaries of 2 Kings 21:13
2 Kings 21:13
13 And I will stretch over Jerusalem the line of Samaria, and the plummet of the house of Ahab: and I will wipe Jerusalem as a man wipeth a dish, wipinga it, and turning it upside down.