Some translations set quotations from the Old Testament farther to the right on the page than the rest of the text. The ULB does this with the quoted words of verse 17.
In verses 3-6, Paul uses many metaphors from war. He probably uses them as part of a larger metaphor about Christians being spiritually at war. (See: [[rc://en/ta/man/translate/figs-metaphor]])
"Flesh" is possibly a metaphor for a person's sinful nature. Paul is not teaching that our physical bodies are sinful. Paul appears to be teaching that as long as Christians are alive ("in the flesh"), we will continue to sin. But our new nature will be fighting against our old nature. (See: [[rc://en/tw/dict/bible/kt/flesh]])