Anyone who represents Lord Caitanya and Kṛṣṇa, he is spiritual master. That's all. Anyone who speaks exactly what Lord Caitanya said, exactly what Kṛṣṇa said, then he is spiritual master. Just like a teacher who says that, "I have passed M.A." Now what is the proof? That means if he speaks exactly like persons who have passed M.A. examination, then he is M.A. A medical practitioner who is approved by other medical practitioners in the medical college, he is medical practitioner.
Similarly, if you want to test who is spiritual master, you have to see the standard spiritual master, Kṛṣṇa and Lord Caitanya and similar. Even Lord Jesus Christ, there are . . . Lord Buddha, they are also spiritual masters, but they spoke in different circumstances. That is different thing. But if you want to know who is a spiritual master, then you have to test him whether he is speaking exactly like the bona fide spiritual master.
Śrī Narottama dāsa Ṭhākura has explained about this, who is spiritual master. What is that? He says, sādhu śāstra guru vākya tinete kariyā aikya (Prema-bhakti-candrikā).
If you want to advance yourself in spiritual science, then you have to test these three things. What is that? Sādhu, saintly person. Sādhu, śāstra, scriptures, and spiritual master.