Elliot R. Wolfson, “Merkavah Traditions in the Philosophic Garb: Judah Halevi Reconsidered,” Proceedings of the American Academy for Jewish Research 57 (1991), pp. 172–242 .  

Excerpt:

“It is generally agreed that the twelfth century was a critical time

when both philosophy and mysticism began to have a greater
impact on the intellectual development of Jews living in central
Europe. On the one hand, ancient Jewish mystical speculation
on the divine chariot (merkavah) cultivated in the Talmudic
and Geonic periods was joined together with a “new” theo-
sophic conception of divinity, and kabbalah took its place on
the stage of literary history. It is assumed, for instance, that
sometime in this century the Sefer ha-Bahir, held by Scholem
and others to be the first text fully dedicated to theosophical
kabbalah, appeared in Provence.1 It was also in this very
geographical region during this century that other, apparently
autonomous, circles of kabbalists appeared on the scene, the
most well-known being the circle of R. Abraham ben David of
Posquieres and his son, R. Isaac the Blind.2″

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