Sri Raghavendra Swamy, in his Purva Ashrama (the life before taking up sannyasa), was known as Venkatanatha. There is an interest incident in this phase of the life of Guru Raghavendra Swamy. It is said that he showed the true power of Agni Suktam mantra to people.
Guru Raghavendra spent a large part of his Poorva ashrama life teaching Sanskrit and the ancient Vedic texts to children. He never demanded any money for his services and endured a life of poverty along with his wife and son.
Once while traveling in Kumbakonam along with his wife and son, Sri Venkatanatha and his family was invited to attend a function. Unfortunately, the hosts thought the family to be poor and wanted them to earn their food by running a chore. So they asked the family to make some sandalwood paste for all the invitees.
Sri Venkatanatha as per his habit was chanting stotras and mantras while preparing sandalwood for Tilaka. When the guests applied this paste, it induced a burning sensation all over their bodies. Surprised by this, the hosts sought a clarification from Venkatanatha.
He replied that the burning sensation was due to the Agni Suktam (hymn for the worship of Agni in the Vedas) that he was chanting while preparing sandalwood and thus eternal power of Vedic Mantras revealed itself.
Those gathered realized that this can happen only when the mantra is chanted with absolute dedication and devotion. The power is enhanced since it was chanted by someone as virtuous and devoted to Bhagavan.
Upon realizing his devotion and power, the host apologized profusely to Sri Venkatanatha and sought his forgiveness.
Sri Venkatanatha then prepared the paste again but chanted the Vedic Mantra to Varuna (Vedic rain god) this time. It has been recorded that when the guests applied this paste, they were awash with a sense of being drenched in rainwater, reaffirming the unparalleled devotion of Guru Raghavendra.