Hermetic Principles (the Kybalion)

[Infinite]

The Kybalion I'm reading by the Three Initiates, they keep quoting "The Kybalion". Why would they quote the same book?

This is explained in the chapter I, page 11 of your pdf file:

In the early days, there was a compilation of certain Basic Hermetic Doctrines, passed on from teacher to student, which was known as "THE KYBALION," the exact significance and meaning of the term having been lost for several centuries. This teaching, however, is known to many to whom it has descended, from mouth to ear, on and on throughout the centuries. Its precepts have never been written down, or printed, so far as we know. It was merely a collection of maxims, axioms, and precepts, which were non-understandable to outsiders, but which were readily understood by students, after the axioms, maxims, and precepts had been explained and exemplified by the Hermetic Initiates to their Neophytes.