Here "the mouth" represents the testimony of a witness. This can be translated in active form. Alternate translation: "If two or three witnesses speak against the person, then you must execute him" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-activepassive]] and [[rc://en/ta/man/translate/translate-numbers]])
Here "the mouth" represents the testimony of a witness. This can be translated in active form. Alternate translation: "but if only one person speaks against him, then you must not execute him" (See: [[rc://en/ta/man/translate/figs-metonymy]] and [[rc://en/ta/man/translate/figs-activepassive]])