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…It is said that the execution of devotional service is so perfect that one can perceive the results directly. This direct result is actually perceived, and we have practical experience that any person who is chanting the holy names of Kṛṣṇa (Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare)in course of time feels some transcendental pleasure and very quickly becomes purified of all material contamination. This is actually seen. Furthermore, if one engages not only in hearing but in trying to broadcast the message of devotional activities as well, or if he engages himself in helping the missionary activities of Kṛṣṇa consciousness, he gradually feels spiritual progress. This advancement in spiritual life does not depend on any kind of previous education or qualification. The method itself is so pure that by simply engaging in it one becomes pure.
Bhagavada-gita As It Is Macmillan Edition 1975
By His Divine Grace A.C. Bhaktivedanta Swami Prabhupada
Chapter 9, Text 2
rāja-vidyā rāja-guhyaṁ
pavitram idam uttamam
pratyakṣāvagamaṁ dharmyaṁ
su-sukhaṁ kartum avyayam
rāja-vidyā—the king of education; rāja-guhyam—the king of confidential knowledge; pavitram—the purest; idam—this; uttamam—transcendental; pratyakṣa—directly experienced; avagamam—understood; dharmyam—the principle of religion; susukham—very happy; kartum—to execute; avyayam—everlasting.
This knowledge is the king of education, the most secret of all secrets. It is the purest knowledge, and because it gives direct perception of the self by realization, it is the perfection of religion. It is everlasting, and it is joyfully performed.
Purport
This chapter of Bhagavad-gītā is called the king of education because it is the essence of all doctrines and philosophies explained before. There are seven principal philosophers in India: Gautama, Kaṇāda, Kapila, Yājñavalkya, Śāṇḍilya, Vaiśvānara, and, finally, Vyāsadeva, the author of the Vedānta-sūtra. So there is no dearth of knowledge in the field of philosophy or transcendental knowledge. Now the Lord says that this Ninth Chapter is the king of all such knowledge, the essence of all knowledge that can be derived from the study of the Vedas and different kinds of philosophy. It is the most confidential because confidential or transcendental knowledge involves understanding the difference between the soul and the body. And the king of all confidential knowledge culminates in devotional service.
The Hare Krishna Movement 