In most cases, "mouth" in the Bible represents thought and logic, especially the kind of active, concrete thought that is connected with speech. The reason for this is pretty obvious, but it also holds when people, for instance, remove a stone from the mouth of a well, which represents gaining access to spiritual ideas. The mouth is used for eating as well as speaking, of course. In those circumstances, it represents our first, most external perception of a new spiritual idea or desire. This also makes sense, mirroring the way tasting food in the mouth gives us an instant impression of the quality of the food.

121. Internal Meaning of Lamentations, Chapter 3

1-66 Description of the combats of the Lord with hells, which were especially from the Israelitish and Jewish church, with despair, because all had been in evils and in falsities therefrom, and against the Lord;, (7, 6)

He invokes the Father that He may not be forsaken and that He may conquer and subjugate these hells. These things in a summary. (13)