Until the heart is empty, it cannot receive the knowledge of God.

When a person comes to take a lesson on any subject, and he brings his own knowledge with him, the teacher has little to teach him, for the doors of his heart are not open. His heart that should be empty in order to receive knowledge is occupied by the knowledge that he already had acquired.
It is not solid wood that can become a flute, but the empty reed. It is the perfection of that passiveness in the heart of the messenger which gives scope for the message from above; for the messenger is the reed, the instrument. The difference between his life and the life of the average man is that the latter is full of self. It is the blessed soul whose heart is empty of self, who is filled with the light of God.
There are many ideas which intoxicate man, many feelings there are which act upon the soul as wine, but there is no stronger wine than the wine of selflessness. It is a might and it is a pride that no worldly rank can give. To become something is a limitation, whatever one may become. Even if a person were to be called the king of the world, he would still not be emperor of the universe. If he were the master of earth, he would still be the slave of Heaven. It is the person who is no one, who is no one and yet all.