The title translates to "The Essence of the Three Secrets". These "secrets" are three sacred mantras that hold the key to liberation in the Sri Vaishnava tradition:
The final verse from the Bhagavad Gita (18.66), where Lord Krishna promises to protect those who surrender only to Him. rahasya traya saram pdf
A 25-letter mantra that focuses on the process of surrender and the ultimate goal of eternal service. The title translates to "The Essence of the Three Secrets"