Diksha or initiation is a must for the performance of any tantric worship. The word ‘diksha’ literally means a process by which the guru transmits the mantra and attenuates or destroys the sins of the disciple. Diksha has been classified by the teachers of tantra into three types – Shambhavi, shakti, and mantri or anavi – depending on the spiritual status of the disciple.
The first of these is done with a mere meet, touch, or conversation with the disciple, as happened in the life of Narendranath, Swami Vivekananda’s pre-monastic name, on his second meeting with Sri Ramakrishna.
In the shakti type of initiation, the guru forces into the disciple his own spiritual power with his divine wisdom, thus awakening the spiritual dimension of the disciple. In this process, the bija-mantra is written by the guru on the tongue of the disciple and the latter at once merges into a vision of his chosen ideal.
And in the mantri or anavi type the guru whispers the mantra into the disciple’s ear.
Constant repetition and meditation on its meaning by the disciple bursts out the hard outer crust of the mantra. This phenomenon is known as mantra-chaitanya. It is the awakening of nada, the eternal sound. At this stage words or letters of the mantra melt in the moving stream of an unbroken vibration called akhanda-nada. This vibration of sound leads to illumination and the aspirant becomes blessed with the vision of one’s chosen ideal. This process has been mentioned in authentic tantric texts like Rudra-Yamala, Vayaviya Samhita, and Vishvasara Tantra.