A question I received: Why does the sensation of the Upper Light evoke both immense pleasure and terrible suffering?
My Answer: This depends only on your qualities and on whether they’re directed toward the goal. If the Light shines inside a Kli that’s prepared and corrected, then you feel It as goodness. And if It shines into an unprepared, uncorrected Kli, then you feel suffering. However, if your direction is towards the goal, this alters your sensation of the Light to joy, because you anticipate the struggle and the achievement of the goal.
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The Path of Kabbalah: Chapter 2.10 – “The Sensation of the Light”
The Path of Kabbalah: Chapter 3.5 – “The Four Phases in the Evolution of the Vessel”