Gematria is based on the fact the Hebrews had no numbers as such but used their letters as numbers -- that is, the letters ARE numbers. Therefore, every word also has numerical value. Gematria is the study of the numerical value of Hebrew words and the relationship of different words with the same numerical value.
One example Crowley and Regardie have used is that the Hebrew words for "love" and "unity" both have the numerical value 13.
666 is not only the number of the Beast of Revelation but the sum of all the numbers on the magic square of the Sun and the numerical value of the word "Elohikam" ("Your God") -- this can be interpreted in several ways. It may be saying that any god we can recognize (Elohikam) and worship (magic square) is not God but the Beast. It may be saying (with W.B.Yeats) that "the Demon is God inverted." It may be saying that with knowledge of the nature of our "enemy" comes awareness of the tools and relationships necessary to "win." It may be saying that the Demon is the door warden of the Divine, preventing the un-prepared from risking too much.
I think Gematria is primarily a way to get us thinking out of the box, to open our perceptions, to show us the essential interconnectedness of the Universe, to get our minds into a more spiritual frame of reference.
My primary reference is Godwin's Cabalistic Encyclopedia. Crowley and Regardie both discuss Gematria in passing.
Godwin's Cabalistic Encyclopedia: A Complete Guide to Cabalistic Magick by David Godwin.
