The Book of Zohar was hidden for generations and it was prohibited to even look at. Kabbalists themselves promulgated this ban. The secret that is concealed within it is the Light that Reforms, but reaching this Light is possible only by breaking through the protective shield arranged by Rabbi Abba who re-wrote this text. When Kabbalists write books, they express the content so that it is concealed in a special garb, which we must penetrate through to reach what is inside. Their writing is a revelation, but while revealing one thing, they conceal two.
They help us with this concealment that brings us closer, by allowing us, to some small degree, to touch this secret. In fact, if there were no concealment, we would not be able to see anything at all. It is similar to an invisible man who cannot be seen until he dresses. But as soon as he puts clothes on, everybody can see him.
In other words, the concealment of Rabbi Shimon by Rabbi Abba helps us to approach this secret! But on the other hand, it leaves us room for work: If you break through this shield, you will find Rabbi Shimon. Rabbi Shimon brings revelation to us from above to below, so he must disguise himself. He wishes to pass it onto everyone but can’t since we are not ready to receive it. Hence, he cries (crying is symbolic of a small spiritual state, Katnut).
This entire enormous system regarded as Rashbi (Rabbi Shimon ben Yochai) is not a “person” but an upper system that is forced to reduce itself (which is regarded as “crying”) because the lower ones are unable to receive anything from it. And how must he adjust himself, make an “adapter” between himself and the lower ones, as if between a wide pipe and the eye of a needle? So, then another system is engaged, which is called Rabbi Abba, a unique soul that is capable of serving as an adapter that connects us to Rabbi Shimon.
Finally, Rashbi’s light becomes revealed through the special system of Rabbi Abba that descends to us in the form of the book called Zohar. It is titled by the name of the source from which its Light derives (Zohar means the upper radiance): the Light of Infinity or the Light emanating from the head of Arich Anpin.
From the 4th part of the Daily Kabbalah Lesson 12/14/10, Writings of Baal HaSulam