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 verses 9-11 and 21 of this chapter, which are words from the Old Testament.
Some translations set prose quotations from the Old Testament farther to the right on the page to make it easier to read. The ULB does this with the quoted words in verse 12.
These terms are used to refer to people who are mature and immature in their faith. Paul teaches that those who are strong in faith need to help those who are weak in faith. (See: [[rc://en/tw/dict/bible/kt/faith]])