Answer: The people who wrote The Book of Zohar were on the highest peak of the ladder of attainment in the spiritual world, and so for them it was simple and easy.
And in truth everything is written in a very soft way, similar to a grandfather who tells his grandson an interesting story, but it is in fact difficult to attain these states. This is the property of the exposition.
Question: Why was it impossible to write it such that everything would be understood and we could read it like any other book?
Answer: We are in this world. How is it possible to understand what doesn’t belong to it?
Suppose that my friend and I know how to read music and I talk with him about musical notes, while you don’t understand anything about it. How could you understand? We don’t have a common language with you; there is not only no conceptual instrument, but also not a common emotional instrument. It is therefore impossible to transmit The Book of Zohar.
From the Kabbalah Lesson in Russian 2/5/17