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.

80. Saying unto me, Fear not, signifies renewal of life. This is evident from the series of things in the internal sense. For John lay as dead, and the Lord, seen as the Son of man, laid His right hand upon him, and said to him, "Fear not." His "lying as dead" signified failure of his self-life; the Lord's "laying His right hand upon him" signified life from Him; therefore His saying to him "Fear not" signified renewal of life; for all who come suddenly from self-life into any spiritual life are at first afraid, but their life is renewed by the Lord. This renewal is effected in this way that the Divine presence, and fear on account of it, are accommodated to reception. The Lord is present, indeed, with all in the universe, but more nearly or remotely according to the reception of good by means of truths with them from Him. For good is that in which the Lord is present with angel, spirit, and man; therefore the extent and quality of good from the Lord with them are what determine the extent and quality of His presence; if the presence goes beyond this, there is anguish and tremor; but by accommodation to reception there is renewal of life (as can be seen from what has just been said and shown above, n. 78. This renewal is what is signified by "Fear not;" also in other places, where it is said by the Lord or by the angel of the Lord when seen:

Fear not (Daniel 10:12, 19; Luke 1:12, 13; 2:8-10; Matthew 28:6, 9-10).

Renewal of life, that comes by accommodation to reception, appears in the spiritual world, when it is presented to view, as a cloud. All societies there are encompassed by such a cloud, denser or rarer according to reception. (That angels are encompassed by a thin correspondent cloud, lest they should be hurt by a nearer influx of the Divine of the Lord, see Arcana Coelestia 6849. What "clouds" are in the spiritual world, and therefore in the spiritual sense, see above, n. 36.)