"And when Moses came to the Tent of Meeting to speak with Him (the Almighty), then he heard the voice speaking with him, from upon the golden lid (kaporet) which was on the ark of testimony, from between the two cherubim; and [G-d] spoke to him" (Numbers 7:89).

When Moses heard G-d's voice in the Sanctuary, a miraculous phenomenon occurred.  Although the divine voice was as loud as at Mount Sinai when all two million people heard it, so loud as to be audible far beyond the confines of the Sanctuary, the sound was miraculously cut off at the Sanctuary entrance and went no further.  Moshe was compelled to enter the Sanctuary in order to hear it (Rashi).

In the works of Chassidism we find a significant explanation as to why it was necessary for the voice of G-d to be cut off at the Sanctuary entrance and go no further:  It is G-d's desire that Man serve Him out of free choice, and that "G-d's voice"—His call, message and teaching—be brought into the world by man's service.

The "voice of G-d" is a revelation of G-d.  A place which the Almighty sets aside as an established location for repeated revelations of G-dliness, a place where His voice is heard again and again, is a place possessing a higher order of sanctity.  Such a place was the Sanctuary, which was named the "Tent of Meeting" because G-d's Presence was regularly encountered there.  G-d's voice, the same great voice that was heard at Sinai, regularly and repeatedly filled the Sanctuary.

If the voice and the speech of the Almighty had gone forth into the world, repeatedly and regularly, then the world would have become one great "Tent of Meeting," a sanctuary in which Man could not choose to go contrary to G-d's wishes.  Man's service of G-d, through free choice, would be impossible.  It was G-d's desire that we transform, through our service—not through divine intervention—an environment in which His Voice is "not heard" into a fitting dwelling place for His presence.