Vyasadev Meditates on Krsna
"Sadhu-sastra-guru: one has to test all spiritual matters according to the instructions of saintly persons, scriptures and the spiritual master. The spiritual master is one who follows the instructions of his predecessors, namely the sadhus, or saintly persons. A bona fide spiritual master does not mention anything not mentioned in the authorized scriptures. Ordinary people have to follow the instructions of sadhu, sastra and guru. Those statements made in the sastras and those made by the bona fide sadhu or guru cannot differ from one another."
Srimad-Bhagavatam 4:16:1 Purport
"If you accept somebody as guru, then you have to corroborate it whether sastra says that he is guru or any saintly person says that he is guru. This is the way. Similarly, when you take a scripture, you have to know it from the spiritual master, whether that is actually scripture, whether it is accepted by the saintly person. Sadhu. Similarly sadhu also, whether guru says, "Yes, he is sadhu." Whether sastra says, "Yes, he is sadhu." There are three things, sadhu-sastra-guru. So to accept one, you have to take the opinion of the other two. Then you'll get the right way."
Srila Prabhupada Room Conversation, 07-18-73, London
"What is spoken in the scripture is accepted by saintly person, and what is spoken in the scripture, the spiritual master explains only that thing. That's all. So via media is the scripture. ... Saintly person means who confirms the Vedic injunction, who accepts. And scripture means what is accepted by the saintly person. And spiritual master means who follows the scriptures. So things equal to the same thing are equal to one another. This is axiomatic truth."
Srila Prabhupada Lecture, 10-18-68, Seattle
"Sadhu sastra, guru vakya, tinete kariya aikya. Spiritual realization can be perfected by three parallel process. Sadhu. Sadhu means saintly persons, who are realized souls, sadhu. And sastra. Sastra means scriptures, authoritative scriptures, Vedic scriptures, sastra. Sadhu, sastra, and guru, a spiritual master. Three parallel line. And if you place your car or vehicle on these three parallel line, your car will go direct to Krsna. Tinete kariya aikya. Just like in the railway line you see two parallel lines. If they are in order, the railway carriages are carried very smoothly to the destination. Here also, there are three parallel lines--sadhu, sastra, guru: saintly person, association of saintly person, acceptance of bona fide spiritual master, and faith in the scriptures. That's all. Then your carriage will be going nicely, without any disturbance."
Srila Prabhupada Lecture, 10-18-68, Seattle
Bhaktivedanta Book Trust. HDG A.C. Bhaktivedanta Swami Srila Prabhupada.
