The idea of a "prophet" is very closely tied to the idea of the Bible itself, since the Bible was largely written by prophets. At a lower level, prophets represent people who teach from the Bible. At a higher level, they represent the Lord as He reveals himself through the Bible. Viewed in a abstract way, prophets represent the holy parts of the Bible themselves, and also represent doctrine drawn from the Bible. The reason we say "largely written by prophets" and "the holy parts of the Bible" is that not all of the books currently included in the Bible have a complete and continuous internal sense. Some -- like Job, Ruth, and Song of Solomon -- are wonderful literary pieces that got included, but which lack the systematic meanings for words and phrases. Others -- the Acts and Epistles, primarily -- are really doctrinal works, the first attempt by others to extract meaning from Jesus' life and words.

Stones in general represent true ideas. Flint is a kind of stone that can be chipped to form extremely sharp edges. To keep the metaphor going we would want flint to be truth that "comes to a point", and in a way that's exactly what it is. According to the Writings, flint represents the "truths of faith" the rules we learn about how to be good people and serve others so that we can apply them as they arise in life. These are relatively black-and-white concepts ("Thou shalt not murder") that help us identify evil desires and arm ourselves against them. This is why flint knives were (and in some cases still are) used for circumcision, which represents purification from our most base love of self and love of the world -- something that must be accomplished by truths of faith.