The book fell into a certain disrepute - quite unjustly - when Sabbatai Zevi used some of its prophecies to support his claim to be the Messiah, and many modern Jews avoid it. Its rehabilitation, mostly by Hasidic scholars, began towards the end of the 9th century.
Gershom Scholem is in my opinion the best modern authority on the Kabbalah, and indeed on much Jewish mysticism. Alas, he died in 1982, but several of his books are still in print and can be found on Amazon.
The thread is morphing into a few strings. On the issue of authenticity of Kabbalah as a tradition (as I posted to some privately) from Adam the first man, through Abraham, author of the Sefer Zetzirah,) the tribe of Levi while in captivity in Egypt, and beyond—Jews believe in the transmission of Torah “From Moses at Mt Sinai” when G-d Himself spoke the first two commandments to the entire nascent nation, and the last 8 through Moses. Encapsulated in the knowledge Moses expounded is all of the Kabbalah. Every “religious law” right down to modern-day Jewish law (”Hey, why can’t a Jew turn on a light switch on the Sabbath—that’s not “Lighting a fire in my tent!?!?”) is contained in Moses’ teachings, albeit in “zip” form. In fact, the Torah, not only the Talmud, is absolutely replete with the secrets of Torah and can be understood on that esoteric, mystical level—evey single letter, word, phrase, and sentence—but you have to know what you’re reading. And you have to be taught. Jews brush aside all of the challenges or proofs one may bring (vis John Locke’s post) because of the fact of transmission of Torah at Sinai, and the faith that every word of real prophesy is true (see Deuteronomy 13:1-4.)
For an insight, and if those not versed in Hebrew can bear the smattering of translated Hebrew words, here is an audio class on this weeks “parsha” the portion of Torah Jews world-wide are studying this week and reading aloud from a Torah scroll on Shabbos. It is the portion of “Ki Tetzei” (”When you shall go out...”) starting with Deuteronomy chapter 26:1. This class usually looks at one or two verses, parses them in Hebrew, and explains them with classical Jewish commentary (also essential in studying the Bible) and elucidates with teachings of Kabbalah. This week: What’s with that commandment to “send away the mother bird??” This is an authentic rendering of how Kabbalah brings out the “soul” of scripture that the original article spoke of:
http://www.chabad.org/multimedia/media_cdo/aid/468769/jewish/Kabbalah-on-the-Bible-Ki-Teitzei.htm
I respectfully posit that if you are studying the Bible (Torah and subsequent books of Prophets and Writings—as canonized by Judaism) in any other language than Hebrew, the language with which G-d spoke and created the universe, then you are missing the truth—on the simple translated level, metaphoric level, homiletic, and “kabbalistic.”