Quabbala is essentially Jewish mysticism, a subject that is difficult to fully grasp since it is enshrouded in deep mystery. Still, you can see signs of quabbala in modern Jewish culture as well as in the ancient text of the Bible, particularly in the Old Testament.
Instead of focusing on what God wants from mankind, quabbala attempts to hone in on the very essence of God. And of course a line of study that seeks to see God behind his mystical veil is controversial, especially among Jews.
Some of the practices associated with quabbala are strikingly similar to other magical traditions (i.e. Wicca). Jews would likely bristle at this comparison, as would many other religious groups. There are stories of rabbis who were able to achieve great magical feats, such as rising up to heaven and consulting with God face-to-face as well as animating a man made of clay (called a golem). Many modern Jews who practice quabbala have been warned to stay away from such magical practices because they are supposed to be exceedingly dangerous.
The controversial history of quabbala includes four rabbis that studied together in an attempt to look upon God. These rabbis of Talmud were driven mad by their studies, either dying from their ailments or living a shell of an existence until their later death.
The appearance of the false Messiah Shabbetai Zevi was another black eye for quabbala. The practice was ultimately outlawed in the seventeenth century by Jewish Rabbis. The only exception was that men over the age of forty, who were married and also had studied the Torah and Talmud could venture into the mystical studies of quabbala.
People who study quabbala view sacred texts like the Torah as highly symbolic, with hidden meanings and messages ferreted about in the narratives. Studying quabbala and the sacred texts will ultimately lead to one learning the very secrets of God.
Many scholars believe the practice of quabbala is tied to the Assyrian and Babylonian captivity of the nation of Israel in ancient times. They believe many of the teachings and practices were bastardized from the captors' culture, being applied to the Jewish customs, traditions and beliefs in innovative ways.
One of the claims of some followers of quabbala is that it predates all religions on the Earth. In fact, they believe that learning all of the secrets of quabbala will unlock the secrets of God like how the Earth and universe were created