Arcana Coelestia # 8089
8089. 'And all the firstborn of my sons I redeem' means that the truths of faith are not to be ascribed to the Lord, but forms of the good of faith. This is clear from the explanation above in 8080, where similar words occur.
Mouth
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.