Here the words "confident expectation" and "certainty" mean basically the same thing. Paul uses them together to emphasize how strong his expectation is. AT: "I am completely convinced" (See: [[rc://en/ta/man/translate/figs-doublet]])
Paul uses the physical "body" to represent his life or the way he lives. AT: "so that I will honor Christ with all that I do" (See: [[rc://en/ta/man/translate/figs-metonymy]])