Yahweh uses a question to scold the people. This question can be translated as a statement. Alternate translation: "These are the same words ... to the west." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Here "mouth" is a metonym for the words spoken by the mouth. Alternate translation: "by the words of the former prophets" or "through the former prophets" (See: [[rc://en/ta/man/translate/figs-metonymy]])