The phrase "once for all" means to finish something completely. You can make this full meaning explicit in your translation. AT: "For when he died he broke the power of sin completely" (See: [[rc://en/ta/man/translate/figs-idiom]] and [[rc://en/ta/man/translate/figs-explicit]])
Just as one cannot force a corpse to do anything, sin has no power to force believers to dishonor God. AT: "as if you were dead to the power of sin" (See: [[rc://en/ta/man/translate/figs-metaphor]])