נפש החיים · Nefesh haChaim — the answer, and it is also Kabbalah

Chaim of Volozhin's posthumously published book: the mitnagdic reply, written by the Gaon's closest student and the founder of the Volozhin yeshiva.

⭐⭐⭐ The most instructive text in this wing, because it is not the book anybody expects. It concedes the metaphysics — God fills all worlds, the world is sustained continuously, human action has cosmic effect — and then argues that precisely because of this, the supreme act is Torah study rather than devekut, and that a person may not act on the immanence they know to be true. Gate 3 says the thing plainly: you may not think it during prayer.

⚠⚠ So the quarrel is not mysticism versus law. It is two Kabbalists disagreeing about what a person is permitted to do with a doctrine they both hold. A wing that printed the Hasidic side alone would have missed that entirely.