Answer: In order to deter those who are not ready to engage in the wisdom of Kabbalah. A person has to ripen before he begins to study. Even people who wanted to study the wisdom of Kabbalah were turned down and had to make great efforts for a long time before being allowed entry to the study.
He was accepted under very strict conditions with all kinds of restrictions. By performing them, he was allowed to gradually become part of a Kabbalistic group, and then he was dedicated to the requirements for the study of Kabbalah. It was explained that this should be done in association with like-minded people who are building together a small, integral, closed society.
In this society, all are equal, all support each other, are included in one another until they dissolve into one single entity in whom they discover the upper world, and begin to study and explore it.
It says that this is what happened to the great Rabbi Shimon Bar Yochai, who later authored The Book of Zohar when he came to his teacher Rabbi Akiva. The latter sent him away three times, claiming that he wasn’t ready to study the wisdom of Kabbalah yet.
From the Kabbalah Lesson in Russian 24/1/16