Paul speaks of the sinful nature of Christians who have refused to live by it as if it were a person and they have killed it on a cross. Alternate translation: "refuse to live according the sinful nature with its passions and desires, as if they killed it on a cross" (See: [[rc://en/ta/man/jit/figs-personification]] and [[rc://en/ta/man/jit/figs-metaphor]])
The word "flesh" here is a metonym for the sinful nature. The sinful nature is spoken of as if it were a person that had passions and desires. Alternate translation: "their sinful nature and the things they strongly want to do because of it" (See: [[rc://en/ta/man/jit/figs-personification]] and [[rc://en/ta/man/jit/figs-metonymy]])
If your language does not have different words for "passions" and "desires," you can treat this as a hendiadys or doublet that simply emphasizes the idea of desires that are wrong, that harm the one who desires and if fulfilled would harm other people. (See: [[rc://en/ta/man/jit/figs-hendiadys]] and [[rc://en/ta/man/jit/figs-doublet]])