Charles Ellicott Commentary Jeremiah 21:13

"Behold, I am against thee, O inhabitant of the valley, [and] of the rock of the plain, saith Jehovah; you that say, Who shall come down against us? or who shall enter into our habitations?" — Jeremiah 21:13 (ASV)

O inhabitant of the valley ... —The noun, as the marginal “inhabitress” shows, is feminine; and, as in “the daughter of Zion” for Zion itself, describes the lower city of Jerusalem, Isaiah’s “valley of vision” (Isaiah 22:1, 5), the Tyropœon of Josephus. The “rock of the plain” (compare Notes on Jeremiah 17:3 and Jeremiah 18:14) is, in like manner, the higher city built on the hill of Zion. The king and his people trusted, as the Jebusites had done of old (2 Samuel 5:8), in what seemed to them the impregnable strength of their natural position. There seems no adequate reason for taking the words as symbolizing the kingly house of Judah, but it is probable enough that local associations, palaces on the hill or in the valley, may have given the words a specially pointed application.