The word "it" refers to the instructions that the writer gives in the previous verse. The full meaning of this can be made clear. The word "flesh" represents the whole body. Alternate translation: "If you do this, it will be healing for your body" (See: [[rc://en/ta/man/jit/figs-explicit]] and [[rc://en/ta/man/jit/figs-metonymy]])
These words form a merism that refers to the entire person through metonymy for the outer man and the inner man. (See: [[rc://en/ta/man/jit/figs-metonymy]] and [[rc://en/ta/man/jit/figs-merism]])