The Book of Zohar, “VaYikra” (The Lord Called), Item 16: And the opening of the Lights of the four letters of Yod-Kof-Reish-Aleph (יקרא) [Yikra, “will call”] is considered a calling and an invitation for Moses to come to the tent of meeting.
The Creator is revealed in a name of four letters. Since our desire is made of four phases, its correction is gradual—from the lightest phase to the darkest, most egoistic one—and it is the gradual revelation of the Light of the Creator that corrects all our desires and fills them. We reveal the name of the Creator, which means that the Creator is revealed in us.
The attainment of the Creator is according to the four letters, according to the four levels of the correction of the ego. The Torah tells us about the Creator’s name, which cannot be pronounced and which is a secret until a person reveals it inside him. Reveal it and the secret will become a revelation.
This name is not expressed since it is impossible to write or to express it as it is revealed inside us. This is a person’s problem, as it is said, “If youth knew and if old age could.”
We cannot tell or show others what each of us attains because the person you want to convey this to must have the matching attributes.
The prohibition of expressing the Creator’s name is not a taboo, but the inability to put the spiritual sensations into words . One can pronounce His name endlessly, but it won’t mean anything to anyone.
This is the reason that most of the holy books were concealed from humanity, so that people would not get confused with anything in them. Now, when our ego is ripe and can use these books correctly, more or less, in order to correct itself, they are revealed to the world.
From KabTV’s “Secrets of the Eternal Book” 10/24/13