Some translations set each line of poetry farther to the right than the rest of the text to make it easier to read. The ULB does this with the poetry in 4:1-9.
The prophecy revealed to Jeremiah is recorded in 3:19-4:3. Despite covering more than one chapter, this should be seen as one unit. (See: [[rc://en/tw/dict/bible/kt/prophet]] and [[rc://en/tw/dict/bible/kt/reveal]])
This chapter prophecies Yahweh's punishment on Judah. This should bring Judah to repentance, but it does not. It is also intended to make the nations fear the power of Yahweh and make them desire to worship him. (See: [[rc://en/tw/dict/bible/kt/repent]] and [[rc://en/tw/dict/bible/kt/fear]])