While the study of Kabbalah (Jewish mysticism) has always been a part of Torah study, it only gained public prominence in the early 14th century when a Spanish rabbi, Moses de Leon, published the Midrash de Shimon bar Yochai, better known today as the Zohar.
According to Rabbi de Leon, the Zohar was a compilation of the teachings of Rabbi Shimon bar Yochai (Rashbi) that were recorded by his son Elazar and his disciples shortly before the great sage’s death. Jewish tradition believes that these teachings were given to him by the prophet Elijah while Rashbi and his son lived in a cave for 13 years, hiding from the Romans.
The origin of the Zohar was, and remains, a controversy. Many believe that it was actually written by Moses de Leon, while others firmly accept de Leon’s attribution of the text to an ancient manuscript by Rashbi.
The Zohar, which means "The Splendor" or "The Brilliance," contains a mystical discussion of God, the structure of the universe, the nature of souls, sin, redemption, good and evil and related topics. It is written in Aramaic and Hebrew, and is structured around the weekly Torah portions. Numerous commentaries have been written that are studied alongside it.
Kabbalah, and thus the Zohar, views the world from a spiritually-oriented perspective. Every action in the world has an equal spiritual reaction that affects the world. Each person has the ability to bring the Divine closer, or to push the Divine away. The mystical allegory in the Zohar is based on the principle that all visible things, including natural phenomena, have both an exoteric reality and an esoteric reality. (If you cannot understand the last few sentences, not to worry, you’re in good company - after all, it’s mystical!)