There is an ironic and devastating play on words in this final verse of the section. The Lord will not turn back
(shuv) because the people have not turned back to him. The judgment is inevitable; nothing will stop it now: the Lord will not relent and for this the earth shall mourn, and the heavens above be dark.
This once again refers to the cosmic themes of the poem in Jeremiah 4:23–26, expressing just how serious and devastating the judgment of Judah will be.
28 “For this the earth shall mourn, and the heavens above be dark; for I have spoken; I have purposed; I have not relented, nor will I turn back.”