Answer:
   
   The Torah is studied on four general levels:
     * The simple meaning of the text
     * Hints and mnemonics
     * Hermeneutics and derivations (from which we get halachah, Jewish
       law)
     * Fundamentals and kabbalah
       
   Gematria is not only used by Kabbalists, but is also useful as a hint
   or mnemonic, as a means of associating some idea with the text of the
   Torah. People who enjoy these things tend to be the same people as
   those who study kabbalah. Neither will appeal to the strict
   rationalist; even if one gives them a rationalist basis. However,
   that's just a psychological tendency. The Tosafist movement (12th and
   13th cent CE) wasn't particularly kabbalistic (in fact, the competing
   pietists movement, Chassidei Ashkenaz was), yet their commentary is
   rife with gematria.
   
   Kabbalah teaches that everything is an intentional act of G-d. Which
   implies that there are no coincidences. Such synchronicisties and
   other "coincidences" are potential learning experience, since G-d made
   them that way for a reason. Numbers are used as symbols, so that the
   number of elements in some commandment, or planets in the sky, letters
   in the Hebrew alphabet or letters of a given type, or whatever, are
   assumed to be chosen by G-d to indicate more about their significance.
   So, for example, it is deemed significant that there are the same
   number of days in the week as colors in the rainbow, both of which are
   one less than the number of days in the harvest festival of Succos and
   the number of strings in a tassle of tzitzis. Seven represents the
   totality of creation, eight is therefore striving to go beyond the
   limitations of this world. Sometimes, gematria is used here as well. A
   tool that is useful as a mnemonic device when studying Torah is a
   source for finding meaning for these coincidences.