This is a passive phrase. You may translate it in an active form with a personal subject. Alternate translation: "Moses wrote" (See: [[rc://en/ta/man/translate/figs-activepassive]])
The logic implied here is that one person can verify the words of another. Alternate translation: "if two men say the same thing, then people know it is true" (See: [[rc://en/ta/man/translate/figs-explicit]])