There is a long tradition of esoteric wisdom among the Jewish people; that is, going back at least as far as the time of the Mishnah, there were certain scholars who believed they possessed higher wisdom about issues of metaphysical importance. They believed this wisdom was meant to be esoteric, only for those who had properly prepared themselves (intellectually and spiritually) for such study. Thus, in a famous story, R. Elazar b. Arakh wanted to study such esoteric wisdom with R. Yohanan b. Zakkai, who refused to teach him until he could prove himself ready. At that point R. Elazar delivered a talk on his understanding of these issues, which was so impressive that the angels came to listen.

Various contenders for the content of that esoteric wisdom existed among the Jewish people—Rambam believed that it was philosophy, but many others saw it as one form of mysticism or other. In a manifestation of one such kind of mysticism, I recall Prof. Soloveitchik once mentioning that a German pietist of the 12^th century complained that the people in his town were unwilling to wait while he not only said his prayers with fervor, but took the time to count the number of occurrences of each letter!

In the sixteenth century, however, Lurianic kabbalah (the kabbalah as taught by the Ari, R. Isaac Luria) became the prime contender for that kind of wisdom, and one of its contentions was that even relatively ordinary actions can have profound consequences on the universe, in particular on bringing about a greater unification of the physical world with the Divine. In that system, the notion of kavannah in prayer took on a new meaning. Whereas before it had primarily meant paying attention to the meaning of the words while reciting them, kabbalistic kavannah referred to having a proper awareness of the mystical impact of those words. The Siddur about which the Noda BeYehuda was asked had printed formulas that would help people have those mystical intentions in mind as they performed the various relevant rituals.

The Noda BeYehuda, rather than answering the question (and explaining what it means to be meyahed shem Kudsha, to unify the Name), forcefully rejects the notion that ordinary people should be saying that formula at all. Although he does not reject kabbalistic belief at all, he makes it very clear that he sees no need for those who are not adepts (meaning who have not become deeply versed in Kabbalistic thought and theology, a study that was supposed to be preceded—as far as Kabbalists themselves were concerned—by a good grounding in traditional Talmud study) to involve themselves in such issues.

Similarly, almost a century before, Havvot Yair (210) had reacted strongly to someone who asked him for basic knowledge about Kabbalistic beliefs. While he displayed at least some knowledge of basic issues of kabbalah, he differentiated kabbalistic knowledge, where creative insight and intellectual innovation is impossible, from Talmudic knowledge, where rigorous study can qualify a person to suggest novel insights.

A phrase that summarizes this wariness of kabbalah or other esoteric knowledge is cited from the book of Ben Sira (see Hagigah 13a), who warns not to examine matters beyond ourselves, adding that we should not involve ourselves in hidden matters. In another responsum relating to prayer, Rashba (5;52) was asked why our blessings are constructed in both the second and third persons (we say barukh atah, blessed are You, and then we say asher kideshanu, who has sanctified us). He notes that the kabbalists suggest a reason for the issue, but refuses to discuss it, because of ein li esek ba-nistarot, hehas no involvement with hidden matters. (Some academics are actually interested by Rashba’s refusal to indulge in kabbalistic study, since his teacher was Ramban, who clearly involved himself in such matters).

Instead, Rashba offers a simple explanation, that the blessings are meant to indicate both God’s immanence and transcendence. That is, we are supposed to always be aware of two facts that seem paradoxical: first, that God is the Creator, indicating a deep connection to the world (melo kol ha’arets kevodo—the world is filled with His splendor) and second that God is completely Other, so different from us as to be incomprehensible to people in any significant way. To assert the truth of both facts, we phrase our blessings in both the present (second person) and the removed (third person).

One more example of the use of "ein li esek be-nistarot" is Radbaz’ explanation of the sin of Adam haRishon where, refusing to entertain kabbalistic views, he suggests that Adam thought by eating of the Eits haDa`at, he would become wise enough to find the Tree of Life, and thus live forever, raising himself (even sinfully) to the level of the angels, heightening his status as a servant of God. Of course, since God did not want this kind of service, he was duly punished.