if i want to use mantra to work i need to get deeksha from guru. What i am asking is Like that if brahma nani want to use mantra to work whether he also need to get deeksha from guru or not.
Deeksha may be or may not be necessary for attaining Brahma Jnana or SELF REALISATION. It depends on the prArabdha of the individual concerned.
1) Ramakrishna "Gadadhar" Chattopadhyay later known as Sri Ramakrishna Paramahamsa had Gurus for initiating him into various methods of worship of the Almighty.
Bhairavi Brahmani initiated Ramakrishna into Tantra,
Ramakrishna took up the practise of vātsalya bhāva under a Vaishnava guru Jatadhari
Advaita Vedantist and Digambara monk Tota Puri initiated Ramakrishna into sannyasa and non-dual meditation
In respect of Sri Anandamayi Ma the following was how she got initiation.
Anandamayi was born Nirmala Sundari Devi on 30 April 1896.
On the full moon night of August 1922, at midnight, twenty-six-year-old Nirmala enacted her own spiritual initiation. She explained that the ceremony and its rites were being revealed to her spontaneously as and when they were called for.
Although uneducated on the matter, the complex rites corresponded to those of traditional, ancient Hinduism, including the offerings of flowers, the mystical diagrams (yantras) and the fire ceremony (yagna).
She later stated, "As the master (guru) I revealed the mantra; as the disciple (shishya) I accepted it and started to recite it."