The prophet is not a man like other men–not because he is a mad or extraordinary person, but because he has thrown off his self-hood and become an empty vessel.
He has become a vessel that God can fill and use.
Moses was the greatest of prophets, able to speak with God because he was the humblest of men on earth.
Because he had become nothing in his conscious existence, his existence could serve the Shechinah properly.
–Rabbi Adin Steinsaltz
From In the Beginning by Rabbi Adin Steinsaltz