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 4:3-4, 7, which is quoted from the OT.
This is probably a reference to a prophesied time when Israel would have peace. This may be physical peace or spiritual peace. (See: [[rc://en/tw/dict/bible/kt/prophet]] and [[rc://en/tw/dict/bible/kt/spirit]])