Source : Guru Mahima
Kabir das had a son by name Kamaal. Kamaal once went to Pandaripur. A Sethji who lived there requested for and received Rama Nama upadesa from Kamaal. In return he gave a diamond to Kamaal. Kamaal returned home to Varanasi and showed the diamond to his father.
Kabir das asked, "Where did you find this?"
Kamaal explained what had happened at Pandaripur. Kabir das beat him black and blue and cried out, "You have sold Rama Nama for a price! Is it for this that you have taken birth as my son? Go back to Pandarpur and throw the diamond back at that man's face."
Kamaal shivered from head to foot. Kabir das also ordered him to bring back the Rama Nama that he had given to the Sethji! Kamaal went to Pandaripur, searched for the Sethji and returned the diamond to him. He then said, "Give back the Rama Nama upadesa that I had given you."
Kamaal said, "The upadesa that I have done is no ordinary one. It has gone deep into you. I will illustrate it to you."
Kamaal then pointed out to a rock nearby and said, "Say 'let the Rama Nama updesa received from Kamaal come out' and spit on this rock." "
When the Sethiji did as bid, the rock jumped about with the sound 'Rama! Rama! Rama! Rama!' for a whole day!
If the fruit of the upadesa received from a Mahan could work into an inert thing what can it not bestow on one who does japa of it? Sankara, in his commentary on one of the Upanishads, says, 'having attained birth as a human being and received upadesa from a genuine Guru if a man does incessant japa of it, without lethargy, he would have the fourteen worlds in his control.'
Please check these: Excerpts from a discourse by our Sri Sri Muralidhara Swamiji
Sathguru threw the arrow of God's name aiming the disciple with full force. That pierced the disciple in such a way that the forest fire of knowledge and separation from God flamed up in which all sensualities have been burnt in to ashes