This is a full translation of an important, but generally neglected, work of theoretical Kabbalah (the most prominent, although not the only, form of Jewish mysticism). It explains in detail the doctrine of the Sefirot (or Sephirot), the creative emanations of the unknowable God. It arranges them in ascending order (toward Divine Totality), rather than the descending order (toward the Created World) in which they are usually presented. It has been suggested that it could, therefore, at least in theory, be used as a meditation guide, although it does not seem to have been considered even devotional reading. (Descriptions of Kabbalistic meditation practices were rarely committed to writing, so the absence of evidence on this point may not be evidence of absence, but so far as I know this is only a reasonable speculation.)
"Gates of Light" is a clear exposition (well, clear for mystical theology), rather than a series of parables to be interpreted, which may account for its being studied, but not often quoted, and not being the subject of commentaries by later Kabbalists. It also suffered from being known as the work of a "modern" writer, in medieval Spain, instead of being offered, like the "Zohar," as a rediscovered text from the time of the Talmudic sages. "Gates of Light" may still be too sparse in language to appeal to devotional readers, but I would hope that those with a personal, spiritual, interest in Kabbalah would use it to improve their grasp of the intellectual foundations of the movement.
Students of the history of Kabbalah, to whom the translation seems mainly directed, will find this translation of great interest. So will students of Kabbalah in history (a slightly different topic). Although the book was eclipsed in fame in its own time and later by the "Zohar," an abridged Latin version was influential in Christian circles during the Renaissance, when ultimately Neo-Platonic theories of divine emanations were extremely popular. Its availability in English is therefore of importance outside the circles of those interested in Judaica, or in Kabbalah in particular.
I have one, relatively minor, objection to this version. For some reason, the translator has chosen to render the technical term for emanations, "Sefirot" (singular form "Sefirah"), as "Spheres," as though it derived from the Greek "sphaira." As Gershom Scholem, among others, demonstrated at length, the actual origin is the root "sfr," originally referring to counting or numbers. The word "sefer," meaning "book" (i.e., an account of things) is the most generally familiar form to those with a little Hebrew. "Sefirah" was also linked, as a significant word-association, with the Biblical word "sappir," meaning a gem (Greek and Latin "sapphire," but not necessarily the modern stone). The pun on "sphaira," the Greek word for "ball" does eventually appear in the literature, but it does not seem likely to have had much currency in thirteenth-century Spain. The translator's decision makes for easier reading, but it could suggest extraneous associations, such as the crystalline spheres of medieval astronomy (and some sort of Kabbalistic astrology). This is indeed a minor objection, but the reader unfamiliar with the field may find the choice confusing, and the subject is already esoteric.