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.

The nature of the soul is a deep and complicated topic, but it can be summarized as our spiritual life — that is, who we are in terms of our thoughts and affections. And that, generally, is the internal sense when the Bible talks of a soul. You could be missing limbs, disfigured in the body due to illness or accident, paralyzed, but you would still be a complete human being. That's because the soul is the real you, and the soul has to do with internal things, not the state of your body.