In a pioneering monograph-length study of the theological journey of Moses ben Shemtov de León of Guadalajara--self-proclaimed "Light of the West" and presumed writer of the Zohar, the kabbalah's crowning literary achievement--Avishai Bar-Asher and Jeremy Phillip Brown reach bold new conclusions about the kabbalah's prominence in medieval Castile. Through rigorous examinations of fragmentary texts inaccessible to scholars previously, the authors unearth critical insights about de León, specifically his regimens of pious living, discourse on gender, understanding of the Hebrew language, and signature thirteen-fold speculation. Bar-Asher and Brown correlate the large body of de León's Hebrew writings with the canonical Zohar, charting the parallel paths of their growth. They also reveal, with unprecedented clarity, the reciprocally interreferential character of the twin corpora at the heart of Castilian kabbalah. Through the exploration of a variety of alternative contexts offering new interpretations of de León's remarkable creativity, Light is Sown offers extraordinary access to the intellectual history of the Zohar and its worlds. Ranging from those of Alfonsine Castile, where the innovation of ancient linguistic theories went hand-in-hand with imperialism and cultural annexation, to Renaissance Italy--where Christian apologists preserved kabbalistic writings that, if not for their intervention, would have otherwise been lost to time and history--the key discoveries and thematic insights offered in Light is Sown yield a timely analysis of one of the most glorious fruits of Jewish theology.