Excellent question, and here is the bottom line: First of all, non-Jews don't need to be practicing Kaballah, because it was never for them. Those with little or no understanding of Torah and the extrabiblical Jewish writings (such as Talmud, Tanya, etc.) will easily misunderstand and distort these teachings. Before reading the rest of our response, please check out this article at Chabad.org so you can understand the Jewish reasoning on Kaballah.
The thing is, the Hebrew language is the Creator's language and the Creator's numbering. It is one thing to see and study YHWH's use of numbers, but it's quite another to use it to "explain mysteries" made by man. Just look at this Wiki definition of Kabbalah: "Kabbalah is a set of esoteric teachings meant to explain the relationship between an unchanging, eternal and mysterious Ein Sof (no end) and the mortal and finite universe (his creation)." Kabbalists have transcended scripture for the mystical - which is actually forbidden in Scripture! (Deuteronomy 18:10-14)
The longer answer to your question is that Kabbalistic Mysticism is a Jewish tradition based on a mixture of myth, magic, numerology and astrology - something that YHWH (Yahweh) abhors and considers to be in the same category as witchcraft, tarot card reading, and fortune telling as they, in essence, strive to answer questions or find solutions to that for which only God has definitive answers.
People who are into Kaballah and the Zohar are caught up in mysticism; something which only leads people away from the Truth of Scripture. Kaballists and their ilk don't deal with Yahweh, the God of the Bible; but, rather, with the god of mysticism - a movement which, as far as Judaism is concerned, started in the Middle Ages with Spanish Jews who spread their ideas throughout the Jewish world and caused people to ignore the obvious meaning of the Scriptures through the use of Numerology and other practices. In order to understand Yahweh, we only need to accept what the Scriptures teach and to employ Bible hermaneutics - allowing the Scripture to interpret Scripture. Traditions of man, including the traditions of the Kabbalah, only serve to lead us astray.
Isaiah 47: 13 You are worn out with all your consultations - so let the astrologers and stargazers, the monthly horoscope-makers, come forward now and save you from the things that will come upon you! 14 Look, they will be like straw! The fire will consume them. They will not save even themselves from the power of the flame. It will not be coals for warming oneself, not a fire to sit beside!
Deuteronomy 17: 2 "If there is found among you, within any of your gates [in any city] that ADONAI your God gives you, a man or woman who does what ADONAI your God sees as wicked, transgressing his covenant 3 by going and serving other gods and worshipping them, the sun, the moon, or anything in the sky - something I have forbidden - 4 and it is told to you, or you hear about it; then you are to investigate the matter diligently. If it is true, if it is confirmed that such detestable things are being done in Isra'el; 5 then you are to bring the man or woman who has done this wicked thing to your city gates, and stone that man or woman to death.
Leviticus 20: 6 "'The person who turns to spirit-mediums and sorcerers to go fornicating after them - I will set myself against him and cut him off from his people...."
Deuteronomy 18: 9 "When you enter the land ADONAI your God is giving you, you are not to learn how to follow the abominable practices of those nations. 10 There must not be found among you anyone who makes his son or daughter pass through fire, a diviner, a soothsayer, an enchanter, a sorcerer, 11 a spell-caster, a consulter of ghosts or spirits, or a necromancer. 12 For whoever does these things is detestable to ADONAI, and because of these abominations ADONAI your God is driving them out ahead of you.
Kabbalistic Mysticism is difficult to describe and has a very complicated history that was originally oral in nature (as was the Talmud, which is the "Oral Torah"), and committed to writing during the Middle Ages in books such as the "Zohar". Many of these writings were alleged to be secret ancient writings or compilations of secret ancient writings.
The bottom line is: Anything that cannot be found in Scripture is NOT the true Word of YHWH, and should be viewed with a healthy amount of skepticism. This includes Kabbalistic Mysticism which CANNOT BE FOUND IN SCRIPTURE (which YHWH "breathed" into being).
To show how difficult and involved the man-made idea of Kabbalah is, we've borrowed the following in-depth information from the traditional Jewish website, Judaism 101:
...Like most subjects of Jewish belief, the area of mysticism is wide open to personal interpretation. Some traditional Jews take mysticism very seriously; it is an integral part of Chasidic Judaism, for example, and passages from kabbalistic sources are routinely included in traditional prayer books. Other traditional Jews take mysticism with a grain of salt. One prominent Orthodox Jew, when introducing a speaker on the subject of Jewish mysticism, said basically, "it's nonsense, but it's Jewish nonsense, and the study of anything Jewish, even nonsense, is worthwhile."
Mysticism and mystical experiences have been a part of Judaism since the earliest days. The Torah (the first five books of Moses) contains many stories of mystical experiences, from visitations by angels to prophetic dreams and visions. The Talmud (Oral Torah) considers the existence of the soul and when it becomes attached to the body. Jewish tradition tells that the souls of all Jews were in existence at the time of the Giving of the Torah and were present at the time and agreed to the Covenant. There are many stories of places similar to Christian heaven and purgatory, of wandering souls and reincarnation. The Talmud contains vague hints of a mystical school of thought that was taught only to the most advanced students and was not committed to writing.
In Hebrew, the word Kabbalah does not have any of the dark, sinister, evil connotations that it has developed in English. For example, the English word "cabal" (a secret group of conspirators) is derived from the Hebrew word Kabbalah, but neither the Hebrew word nor the mystical doctrines have any evil implications to Jews.
According to Kabbalah, the true essence of G-d is so transcendent that it cannot be described, except with reference to what it is not. This true essence of G-d is known as Ein Sof, which literally means "without end," which encompasses the idea of His lack of boundaries in both time and space. In this truest form, the Ein Sof is so transcendent that It cannot have any direct interaction with the universe. The Ein Sof interacts with the universe through ten emanations from this essence, known as the Ten Sefirot.
These Sefirot correspond to qualities of G-d. They consist of, in descending order, Keter (the crown), Chokhmah (wisdom), Binah (intuition, understanding), Chesed (mercy) or Gedulah (greatness), Gevurah (strength), Tiferet (glory), Netzach (victory), Hod (majesty), Yesod (foundation) and Malkut (sovereignty). The middle five qualities are mentioned explicitly and in order at I Chronicles 29:11: Yours, O L-rd, is the greatness (gedulah), the strength (gevurah), the glory (tiferet), the power (netzach), and the splendor (hod). I have seen this passage translated in widely varying ways, but the Hebrew corresponds to the names of the Sefirot in order. The Ten Sefirot include both masculine and feminine qualities. Kabbalah pays a great deal of attention to the feminine aspects of G-d. The Sefirot are commonly represented in a diagram (that basically resembles a star chart - You can see it at the website mentioned above). This diagram is commonly known as the Tree of the Sefirot or the Kabbalistic Tree of Life. There is great significance to the position of these various attributes and their interconnectedness.
The Sefirot are not separate deities, as some might think by taking this too literally. They are intimately a part of G-d, and yet they are in contact with the universe in a way that the Ein Sof is not. The Sefirot connect with everything in the universe, including humanity. The good and evil that we do resonates through the Sefirot and affects the entire universe, up to and including G-d Himself....