Premanand Maharaj Ji
How should I express gratitude to my guru?
Balihari, not a formal thank-you
Thank-you is said to others, not to our parents, and the guru is like a mother and our own soul. Balihari is different from dhanyavad: it is said inwardly to his nature and his compassion.
Thanks are given to others. One never thanks one's own parents. One does not thank such a Sadguru either.