Sri Ramanuja Acharya lived from 1017–1137 AD. He was deeply moved by the bhakti (devotion) of the Alvar poet saints and strongly disagreed with the impersonal notion of God that was popular during His early studies. Later on, after successfully debating His challengers, He formalised the Sri Sampradaya based on the idea of devotion to a personal God in the form of Sriman Narayana. The Sri Sampradaya is the oldest and largest Vaishnava lineage.
The Grace of Om Namo Narayanaya
Om Namo Narayanaya is the main mantra of Sri Vaishnavism and Bhakti Marga. This once-secret mantra was originally made available to the world through the Grace of Ramanuja Acharya.
Paramahamsa Vishwananda offers initiation into this mantra through the Bhakti Marga Spiritual Order and Atma Kriya Yoga. Initiation gives the Grace to attain God-realisation when the mantra is lovingly practised with bhakti. He also shares this mantra through a free practice called Project Mantra.
Story of the Secret Mantra
Ramanuja made 17 pilgrimages of great distance to try and obtain the secret mantra, Om Namo Narayanaya. Each time the Guru refused Him, saying He was not worthy.
Finally, on the 18th trip, the Guru agreed to give Him the mantra, but only on the condition that He would never share it with anyone. He agreed. However, upon hearing the mantra, He realised its power to liberate souls from the cycle of birth and death. He immediately climbed to the top of the temple, calling everyone to come. When they all gathered, He shouted the mantra three times from the rooftop, thus giving it away freely to all.
The Guru was furious and wanted to curse Him to go to hell. But, when Ramanuja said He was happy to go to hell if His actions saved others from the same fate, the Guru realised the truth of His wisdom and begged for forgiveness.