These things are described there. And the sādhu, saintly person, beginning from Vyāsadeva, Nārada, down to many ācāryas, Rāmānujācārya, Madhvācārya, Viṣṇu Svāmī, and latest, Lord Caitanya, in this way, they have accepted, "Yes. It is spoken by Kṛṣṇa." So this is the proof: if saintly persons have accepted. They have not denied. Authorities, they have accepted, "Yes." This is called sādhu.
And because sādhu, saintly persons, have accepted, therefore it is scripture. That is the test. Just like . . . it is common sense affair. If the lawyers accept some book, then it is to be understood that this is law book. You cannot say that "How can I accept this is law?" The evidence is the lawyers are accepting. Medical . . . if the medical practitioners accept, then that is authoritative medical book. Similarly, if saintly persons are accepting Bhagavad-gītā as scripture, you cannot deny it.
So sādhu śāstra: saintly person and scriptures, two things, and with spiritual master, three, three parallel lines, who accept the sādhu and the scripture. Sādhu confirms the scripture and spiritual master accept the scripture. Simple process. So they are not in disagreement. 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. Just like lawyer and the litigants—via media is the law book. Similarly, the spiritual master, 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 scripture.
So things equal to the same thing are equal to one another. This is axiomatic truth. If you have got hundred dollars, and another man has got hundred dollar, and if I have got hundred dollar, then we are all equal. Similarly, sādhu śāstra guru vākya, when these three parallel lines in agreement, then life is success.