138 Openings of Wisdom
In this book, the Ramchal systematically explains both the Kabbalistic metaphor and its meaning, as well as clarifying many apparent contradictions between the Zohar and the writings of the Ari. This is a work for serious students, who should expect to read it more than once in order to fully understand its inner meaning.
Written by Rabbi Moshe Chaim Luzzatto. Translated by Rabbi Avraham Greenbaum. Hardcover, 482 pages.