Main Kabbalistic Sources: Baal HaSulam’s Commentaries on the works of the ARI and The Book of Zohar
Indeed, I know the reason: It is mainly because faith has generally diminished, specifically faith in the holy men, the wise men of all generations. And the books of Kabbalah and The Zohar are filled with corporeal parables. Therefore, people are afraid lest they will lose more than they will gain [from their study, and they will receive a greater breaking or egoism rather than correction], since [by reading what is written in the corporeal images] they could easily fail with materializing [rather than imagining the spiritual properties].
And this is what prompted me to compose a sufficient interpretation to the writings of the Ari [TES], and now to the Holy Zohar [Perush HaSulam]. And I have completely removed that concern [of possible incorrect and, therefore, harmful study of the Torah], for I have evidently explained and proven the spiritual meaning of everything, that it is abstract and devoid of any corporeal image, above space and above time, as the readers will see, to allow the whole of Israel to study The Zohar and be warmed by its sacred Light. [This means that, if one studies The Book of Zohar with the Sulam Commentary, he does not need to fear losing his way to the purpose of creation: adhesion with the Creator.]
– Baal HaSulam, “Introduction to The Book of Zohar,” Item 58