If Vaishnavism is so popular and wide spread in India, the credit must go to Sri Ramanuja, who took advantage of the ecstatic outpouring of the south Indian mystics, the Alvars, and produced a highly logical philosophy of knowledge soaked in devotion as the easiest means of God-realization.
I am the thread that runs through all these pearls, and each pearl is a religion or even a sect thereof. Such are the different pearls, and God is the thread that runs through all of them; most people, however, are entirely unconscious of it.
-Swami Vivekananda