This can be stated in active form. Alternate translation: "not because what I said in my letter distressed you" (See: [[rc://en/ta/man/jit/figs-activepassive]])
"so you suffered no loss because we rebuked you." This means that although the letter caused them sorrow, they eventually benefited from the letter because it led them to repentance. Alternate translation: "so that we did not harm you in any way" (See: [[rc://en/ta/man/jit/figs-idiom]])