Pradyumna: "Now this sādhana-bhakti, or practice of devotional service, can also be divided into two parts. The first part is called regulative principles. One has to follow these different regulative principles by the order of the spiritual master or on the strength of authoritative scriptures."
Prabhupāda: Yes. The regulative principles means that you don't manufacture anything. Regulative principle means authorized—as they are mentioned in the authorized scriptures and as it is confirmed by the spiritual master. Because we do not know. When it is confirmed by the spiritual master, yes, it is right. Sādhu guru, sādhu-śāstra-guru-vākya, tinete kariyā aikya. The same statement of Narottama dāsa Ṭhākura. Sādhu, principles which are followed, sādhu-mārga-anugamanam. We cannot follow asādhu-mārga. We must follow sādhu-mārga. Mahājano yena gataḥ sa panthāḥ (CC Madhya 17.186). We cannot follow an upstart, manufacturing some song, manufacturing some ideas. We cannot follow that. What is authorized song, we shall sing. What is authorized method, we shall follow. Sādhu-guru-śāstra-vākya. Sādhu and guru means on the basis of śāstra. And śāstra means the statements of sādhu and guru. Therefore sādhu and guru and śāstra, they are identical. So they must be corroborated. If somebody's sādhu is speaking against śāstra, then he's not sādhu. If somebody's guru, if he's going against śāstra, then he's not guru. And śāstra means the original guru and sādhu. What do you mean by śāstra? Just like in Śrīmad-Bhāgavatam. Śrīmad-Bhāgavatam means we are studying the character of original sādhu and guru. Just like Prahlāda Mahārāja, Prahlāda-caritra, Dhruva-caritra, Ambarīṣa-caritra, the Pāṇḍavas, Bhīṣma. So Bhāgavata means the glories of Bhagavān and bhaga, devotees. That's all. This is Bhāgavatam. So sādhu-guru-śāstra-vākya, tinete kariyā aikya.
So this is sādhana-bhakti. We must take instruction from the spiritual master. Ādau gurvāśrayam, sad-dharma-pṛcchāt. Who requires a spiritual master? One who is inquisitive of sad-dharma, not asad-dharma. Sad-dharma-pṛcchāt. Tasmād guruṁ prapadyeta jijñāsuḥ śreya uttamam (SB 11.3.21). A man requires a spiritual master when he's inquisitive to know about the transcendental subject matter. A spiritual, a spiritual master... To accept a spiritual master is not a fashion. Just like we keep a dog, pet, similarly, if we keep a spiritual master, pet spiritual master, to get sanction of all my sinful activities, that is not accepting spiritual master. Spiritual master means tad viddhi praṇipātena paripraśnena sevayā (BG 4.34). You should accept a spiritual master where you think that you can surrender yourself fully, and offer his, your service. That is spiritual master. Sādhu-mārga-anugamanam. Sad-dharma-pṛcchāt. So spiritual master is required for a person who is interested in the transcendental subject matter. Tad viddhi praṇipātena paripraśnena sevayā. Tad-vijñānārthaṁ sa gurum eva abhigacchet (MU 1.2.12). Tad-vijñāna, that vijñāna, the science of spiritual life. One who is interested in the science of spiritual life, not that to keep a spiritual master as a fashion. No. One must be serious. Tasmād guruṁ prapadyeta jijñāsuḥ śreya uttamam (SB 11.3.21). First of all, one must know in which subject matter he's inquisitive, in material things, or in spiritual matters. If he's actually interested in spiritual matter, then he should search out a proper, bona fide spiritual master. Gurum eva abhigacchet. Must find out. It is not option. It must. Must, you cannot avoid it. Without bona fide spiritual master, you cannot go a step forward.