Question: Is it possible that the spiritual world exists only in Kabbalists’ imagination? What is the guarantee that it is real?
Answer: Nobody can promise you and give guarantees that the spiritual world exists more realistically than our world.
However, the fact that our world is not real has already been revealed by Kabbalists. They feel this by being above our illusory world, and they understand that this world is created in such a way on purpose, so that we would push ourselves away from it and exit into the real world.
The upper spiritual world is real because we attain the Creator in it, the only driving force, “There is none else besides Him.” By revealing in the spiritual world the force that governs everything, we determine that it really exists.
From the Kabbalah Lesson in Russian 2/25/18