Two big reasons come immediately to mind. First, in most of the places where Jews have inhabited over the last two millennia, outsiders have oppressed and murdered them for very little cause. There was an intense antipathy between Greeks and Hebrews in antiquity, which has since been uncritically adopted by the Romans, the Seleucids, Byzantines, Helenized Christians and Muslims, and from there, Christians and Muslims in general. For most of the previous millenium, Christians were worse than Muslims in oppressing Jews, but just when the Christians became more humane (in the Enlightenment era--- and we Freemasons had a significant role in this), Muslims became crueler. While no Muslim regime has been as awful as the Christian Russian Empire (let alone Central and Eastern Europe of the middle of the last century: we rightly condemn the Germans, but Hungarians, Rumanians, Croats, Ukranians, some Poles and Italians, and others were pretty awful as well), since the establishment of the State of Israel, people in many Muslim countries have gone insane with anti-Semitic rage. If they are mad at the State of Israel, so be it, but to murder their own people who are Jews is another issue entirely. Yemen and Iraq, which have had Jews for thousands of years, are expelling their last Jews these days, and Jews are being abducted and murdered throughout the Ummah, from Pakistan to suburban Paris. The Protocols of the Elders of Zion have been bestsellers in Syria, Egypt, Iran, and Saudi Arabia, (as well as Russia) and even made into a mini-series in Syria and Egypt. The Protocols condemn Freemasonry as well, so wherever people believe this forgery to be real, not only does hatred towards Jews increase, but hatred towards the Craft increases as well.
The result of this has been that Jews have historically felt less-than-comfortable appearing too strange to the majority inhabitants of the countries they dwell in. Polygamy, while historically part of Judaism, was outlawed by Rashi, a Medieval French rabbi. Public parades on Purim have historically inspired pogroms. While the Koran insists that a Muslim show some respect to believers of the other "Religions of the Book" (namely Christianity and Judaism, the other Abrahamic faiths), there is no such restriction in the Christian Gospels, and Jesus' intelligent critiques of Pharisaic Judaism have in the past been warped to convey a hatred for Judaism that Jesus never intended (himself being Jewish). Jews who chanted all night, or were found in the woods performing Hitbodedut were often exposed to violence as a result.
Deeper than this, Jews became deeply discouraged. They wondered why their Messiah did not come and save them through their awful hardships. Isolated in ghettoes, they became frightened and superstitious. Waves of false Messiahs arrived, seducing the populance with wild mystical techniques, only to be dashed down to ignominity, dragging their followers with them. Mysticism in general began to be associated with false Messianism.
The second reason is an internal censorship that is part of a long dialogue between mystics and clerics in Judaism, and has been the cause of many Jewish movements, like Hasidism, Reform Judaism, Reconstructionist Judaism, and Jewish Renewal today. Mysticism is a powerful force to shake things up. Anyone who reads the Prophetic books of the Old Testament knows that the Prophets were not kindly received by the Kings of Israel and Judea. Reading Ezekiel and Elijah, we see the visions produced by their mystical schools. The earliest Kabbalah schools studied the Prophets intently, trying to learn their techniques, but this was deeply frowned upon by the authority figures of their day. Many of their techniques remind me of Kundalini Yoga.
There were three power structures historically in Judaism, none of which were sympathetic to such mysticism. The king, the Kohanim (or priesthood), and the Rabbis. Kings and prophets disagreed, so for people to adopt techniques that would generate prophecy was not in the interest of the monarchy. The Kohanim had a monopoly on ritual animal sacrifice, ritual holiday observance (which often included animal sacrifices, like the Passover lamb and the Yom Kippur scapegoat), and the control of the Temple, including the Sanctum Sanctorum, or Holy of Holies. Mysticism, in contrast, is egalitarian. The Hebrew Prophets were common-born people, sometimes poor or unlearned, and ran roughshod over tradition, especially when observed sanctimoniously or hypocritically. For those of you who are Christian, the image of Jesus casting the money-changers out of the Temple gives an example of the conflict between mysticism and the Kohanim. The rabbis were not as hostile as the other power groups, but they very clearly wanted whatever mysticism that took place to occur under their leadership and guidance, and would declare a mystic an apostate if the mystical practice looked too different from traditional religious practice.
In the last few centuries, two big movements have had mysticism or anti-mysticism as their focus. The first is Hasidism, and the second is Haskalah, often called "The Jewish Enlightenment". Hasidism was a response to the false Messiahs, Sabbatai Zevi, and Jacob Frank. While these men failed, their followers learned Kabbalah and other mystical techniques from them, and wanted to incorporate these ideas into their religious practice when they returned to traditional Judaism. A school of Kabbalists settled in Ts'fat (in modern-day Israel) and under the tutelage of Rabbi Isaac Luria, they created Kabbalah in its modern form (this is a controversial statement which the reader is free to disagree with).
There was an earnest attempt in Eastern Europe to fuse Lurianic Kabbalah and Orthodox Judaism, and Hasidism was the result. This was bitterly opposed by the rabbinical authorities at the time. The founder of Hasidism, Rabbi Israel ben Eliezar, the Baal Shem Tov (master of the Good Name), taught Kabbalah even to those unlearned in Talmud, which was very threatening to a Yeshiva structure that placed great importance on Jewish law. The Baal Shem Tov was more egalitarian, less careful with particulars, and demanded that passion be the center of religious devotion. His followers began to tell fantastic tales about him and his students, and this was very worrisome to the Mitnagdim (or opponents of Hasidism). While some Mitnagdim, like the Vilna Gaon, were themselves Kabbalists, they were very strict about who got taught their techniques, whereas the Baal Shem Tov and his students would teach to anyone who would listen. Hasids tended to be more superstitious, poorer, and certainly more oppressed than the Mitnagdim, who worried that Hasidic mysticism would ruin minds, dilute scholarship, and bring the wrath of the surrounding Christians upon all the Jewish people, not just the wild mystical ones. Indeed this division among the Orthodoxy between Hasidim and Mitnagdim only began slightly to abate when both groups became vastly outnumbered by non-Orthodox Jews, and still further when the Holocaust forced both groups to work together.
Haskalah was a response to Jewish integration and desegregation, which happened slowly as a result of the Enlightenment. Jews were being invited to become Freemasons, and from there were gaining civil rights and some freedom in Europe. Some Jewish writers were enjoying success and a readership among the surrounding Christians, and were finally being allowed to attend university, to own property and to socialize outside the ghetto. There was a sense that this opportunity might snap shut hard unless Jews were willing to conform to the societies they were being invited into, and much reflection took place about how deeply to integrate. While the biggest result was Reform Judaism, even the Orthodoxy was shaped by Haskalah. Reform Judaism sought to question the more fundamentalist aspects of the Jewish religion, and to have reason govern faith. The dietary laws were abandoned, prayers were translated into the language of the country of residency, and Yiddish was abandoned. There was a ruthless excising of superstition (or what was believed to be superstition, whether it was or not), and a lot of social conformity. In Germany and the USA, synagogues clamored to mimic the prominent Protestant Churches of the affluent, even putting in pipe organs and pews in the synagages.
Some of the methods of the leaders of the Reform movement were fairly hostile to other Jewish communities, such as holding a banquet for the Jewish community and feeding forbidden foods to everyone. This created a backlash, which formed into Conservative Judaism. The Reform movement, and to a lesser extent, the Conservative movement, was so ruthless about abolishing superstition and what were felt to be the side-effects of ghetto phobias, that they became very anti-mysticism as a result. If it didn't look analoguous to something their wealthy Protestant neighbors were doing, it often was abandoned.
Thus, by the 20th century, a majority of Jews had abandoned mystical and esoterical practices, and saw them as an embarrassing hold-over of more primitive times. But in Europe, this conformity and respectablity did not save them from the gas chambers. They died alongside the Hasids they saw as throw-backs from a more primitive time. When the survivors emerged on safer shores, they brought with them either the tiny fragments of what remained of the mystical tradition, or a new-found respect for those who held these traditions. With the spiritual crisis of the second half of the 20th century, there was curiosity about these traditions, and whether or not they had anything to say to a world thirsting for more authentic spiritual experiences. Rabbi Abraham Joshua Heschel, a scion of a Hasidic family, and a survivor of the Holocaust, established a Mysticism department at the Jewish Theological Seminary in New York, and Gershom Scholem did the same at the Hebrew University in Jerusalem. Both men were regarded very critically by their peers, and met with a great deal of resistance, but influenced generations of students, including my rabbis.
By the 1960s, two forces moving in opposite directions collided. In one direction, there were mystics seeking a modern audience. Chabad, a Hasidic movement from the 18th century, began doing a lot of outreach under the leadership of their last rebbe, Menachem Mendel Schneerson. He believed that the Messianic Era was at hand, and that all Jews needed to be educated about their religion, to be brought back into Orthodoxy, and to be introduced to a mystical curriculum to enlighten them, in order to prepare for the coming of the Messiah. His outreach was enormously successful, but also inspired other Jewish groups to pay more attention to Jewish mysticism. Two of his emissary rabbis, Rabbi Shlomo Carlebach, and Rabbi Zalman Schachter-Shalomi, began by doing college outreach, and ended up leaving Chabad and forming their own groups, more liberal and open than Orthodox Judaism, allowing Jews of the Reform and Conservative traditions to enjoy the mysticism they had learned as Hasids. The philosopher Martin Buber had romanticized Hasidism in order to describe a Jewish mysticism that Buber felt was vital for his time. While not accurate (and not intending to be accurate), his description was very evocative, and inspired many Jews to seek a deeper understanding of Jewish mysticism.
The other force were young Jews unhappy with the stale liturgical regurgitation pushed upon them in their b'nei mitzvot. Some looked to other traditions to find what the could not find at home. Others, thankfully, looked within Judaism for what they were seeking, and found it there in detail vaster than they had dreamed. The process of incorporating the rich history of Jewish mysticism back into regular worship is daunting, but fascinating. We have a nearby rabbinical seminary run by a Jewish mystic, with one of the largest collections of mystical writings outside of Israel. We regularly have rabbinical interns who are very well-educated in Jewish mystical traditions, and we encourage them to share with us what they have learned, and to show us parallels in other faiths.
At my synagogue, we have had rabbis who were Zen masters visit and show how Zen is similar to Jewish meditation. We have other Jewish Buddhists show how to be syncretist without violating either religion. We have had Sufis come, and show how much of Sufi tradition is actually Jewish originally. At a given Friday night service, or Saturday morning Torah Study, there will be Jews, but also a few Muslims, Christians, Buddhists, Unitarians, syncretists of various stripes, all doing a specifically Jewish ritual that speaks to their conditions. The D'var Torah may do a textual analysis of the weekly parashah, a kabbalistic midrash, a funny personal observation, or a mix of all of them. While the liturgy is in Hebrew, and the traditional psalms are sung, we all enter with different levels of learning and different levels of observance, but all are welcome. We are actively involved in interfaith dialogue, and have active conversations with Christians and Muslims about our similarities and differences, treating each other as cousins rather than strangers. My synagogue is explicitly LGBTQ friendly, and when passages come up in the Torah that address them in a negative light, there is always a lively, humane, respectful discussion.
There is not much explicit instruction in mystical techniques, except for a Monday night Jewish meditation class. The layout of the main chapel incorporates the Tree of Life, and during the Amidah prayer, we are encouraged to stand near the s'firah that best resembles the condition we find ourselves in. There is a lot of encouragement to read Kabbalistic texts, and with the encouragement of some of the leadership of the synagogue, I have read some of the works of Rabbi Moshe Cordovero and Rabbi Moshe Chaim Luzzatto. I am currently interested in the Jewish ethical practice called Mussar, and both authors combine mysticism and ethics in a compelling way. I will blog about Mussar in more detail, because it is fascinating, exports nicely into other traditions, making it something easy to share with non-Jews looking for an ethical practice.
I had originally intended to give an example of Kabbalistic textual analysis, but this post is long enough as it is. Hopefully I will share more later.