I. Kabbalah and Halakhah
The role of kabbalistic mysticism in normative Jewish practice is complex. For someone skeptical of the kabbalistic enterprise, it may even be frustrating. However, a fairly authoritative approach to the role of kabbalah in Jewish law should serve to alleviate many of the concerns.
Traditionalists accept the Zohar, the source of many kabbalistic practices, as a Tannaitic work from the school of R. Shimon Bar Yochai. However, modern scholarship dates the work to Medieval times (link). The more historically sophisticated traditionalists adopt a compromise position–a core of the work is ancient but much has been added over the centuries. While ostensibly this debate should greatly impact the role of kabbalah in halakhic decision-making, there is good reason to render this issue entirely irrelevant.
II. Tefillin and Kabbalah
Two case studies regarding tefillin should establish the relevant attitude. Rishonim, Medieval authorities, debate whether we are obligated to wear tefillin on Chol Ha-Mo’ed, the intermediate days of the holiday (see Tosafos, Menachos 36b sv. yatzu; Rosh, Hilkhos Tefillin no. 16; Rashba, Responsa no. 690 – link ). Important authorities note this debate and add that since the Zohar states not to wear tefillin on Chol Ha-Mo’ed, we should follow that view. R. Yitzchak Karo, uncle of the Beis Yosef, writes that if kabbalists disagree with the Talmud, we must reject their ruling and follow the Talmud. However, if the kabbalists side with one view in a post-Talmudic debate, as in the case with tefillin on Chol Ha-Mo’ed, we allow kabbalah to decide between the disputing parties (Responsa Beis Yosef, end – link). Even those who disagree on this specific case can agree with the approach in general.
On Rosh Chodesh, the prevalent practice is to remove tefillin before the additional Musaf prayers. The Radbaz (Responsa, vol. 4 no. 80 – link) rules that this practice is permissible because it does not contradict a Talmudic ruling. However, since it is based entirely on Kabbalah, we cannot force anyone to follow it. He writes, “I do not instruct anyone to remove or not remove.”
III. Optional Kabbalah
Significantly, the Mishnah Berurah (25:42), quoting an earlier source, explicitly endorses these attitudes. He writes:
The Kenesses Ha-Gedolah wrote in his rules of authorities that anything on which kabbalists and the Zohar disagree with the Talmud and codes, follow the Talmud and codes. However, if the kabbalists are strict we should also be strict. But if it is not mentioned in the Talmud and codes we cannot force people to follow it even though it is mentioned in kabbalah. We should follow the words of kabbalah regarding a rule that is not contradicted by the Talmud and codes. And when authorities disagree, the words of kabbalah should decide.
Many counter-examples can be raised that imply kabbalistic practices are mainstream and mandatory. While I do not wish to speak overly broadly, I can confidently state that, according to this approach, practices based on post-Talmudic kabbalah are generally not mandatory, even if some authorities report them as normative. They are optional, albeit possibly praiseworthy and important.
There is another approach that sees any practice that does not contradict the Talmud as obligatory (see Kaf Ha-Chaim 25:75 for the two views – link). However, the approach we described is perfectly acceptable. A good recent example of this attitude can be found in R. Mordechai Eliyahu’s Imrei Mordekhai (vol. 1 no. 1). After listing over a dozen examples of laws from across the Shulchan Arukh influenced by kabbalah, he cites the above general rules and others which yield the result that while many kabbalistic practices are widespread and deeply ingrained, they are often optional.
IV. Zohar As An Important Text
I see two main theological avenues of explanation for this attitude toward kabbalah and halakhah. The first accepts kabbalistic texts as ancient and authoritative. However, the traditional attitude toward kabbalah restricts its knowledge to the intellectual elite. If you aren’t required (or permitted) to know something, you cannot be obligated to follow it.
However, if there are non-kabbalistic reasons to follow a particular practice, such as a debated understanding of the Talmud and its laws, then the learned authorities who must decide the dispute can/should allow kabbalah to influence their conclusions. This all assumes full acceptance of the kabbalistic authority of the Zohar. Even if it is ancient and holy, it need not be the guide of our daily lives.
Another possible explanation may be more palatable to those academically inclined. Even those who believe that the Zohar was composed by a (or many) Medieval scholar(s) must admit that the author was a brilliant and influential rabbinic thinker. He (or they) certainly attained the status of a Rishon, an important Medieval authority. The Mishnah Berurah‘s rules fit perfectly with this attitude. In a dispute of Rishonim, the Zohar is considered a decisive Rishon who (generally) settles the debate. Like we would a Rishon, we disregard the Zohar if it seems to contradict the Talmud. And if the Zohar proposes a new practice, it can only be optional, even if currently mainstream.
Whether the Zohar is a sacred book from Talmudic time or a Medieval work, its influence in Jewish law is similar. It has an important but not overriding status. Most significantly, it can, but need not, be treated as a source for unique practices.