Excerpt from Sri Chinmoy's book, The Master and the Disciple.
When the disciple and the Master find themselves safe in one another’s heart, the hour of initiation is fast approaching. When the Master initiates someone, he gives that person a portion of his life-breath. At the time of initiation, the Guru makes a solemn promise to the individual seeker and to the Supreme that he will do his best to help the seeker in his spiritual life, that he will offer his heart and soul to take the disciple into the highest region of the Beyond. The Master says to the Supreme, “Unless and until I have brought this child to You, I shall not leave him; my game shall not be over.” And to the disciple he says, “From now on, you can count on me; you can think of me as your own.”
At the time of initiation, the Master actually takes on the disciple’s teeming imperfections, both from the present incarnation and from past incarnations. Of course, there are real and sincere spiritual Masters as well as false Masters. Here I am speaking about the true Masters. Some Masters who are very sincere only initiate one disciple a month. After they initiate the disciple they fall sick and suffer terribly, because they have actually taken on the disciple’s imperfections. Again, there are some spiritual Masters who are able to initiate many disciples without suffering, because they have the capacity to throw the imperfections they take on into the Universal Consciousness. But again, there are some false Masters who initiate fifty, sixty or a hundred disciples at a time, or who initiate by proxy. But this kind of mass initiation is an absurd deception.
The Guru can initiate the disciple in various ways. He can perform the initiation in India’s traditional way, while the disciple is meditating. He can also initiate while the disciple is sleeping or when the disciple is in his normal consciousness, but calm and quiet. The Guru can initiate the disciple through the eyes alone. He will look at the disciple, and immediately the person will be initiated—but nobody will know. A Master can also perform a physical initiation, which is to press the head or the heart of the disciple. At this time, he tries to make the physical consciousness feel that initiation has taken place. But along with this physical action, the Guru will initiate the disciple in a psychic way. At that time the Guru sees and feels the soul of the disciple and acts upon the soul. initiation can also be done by occult processes or in a dream. If there is no spiritual Master available at the time, God Himself can take a very luminous human form in your dream or during your meditation and can initiate you Himself. But this is very rare. Most of the time initiation is done by a Master.