Key topic for discussion is Bhagavad-gita 9.2
राजविद्या राजगुह्यं पवित्रमिदमुत्तमम् । प्रत्यक्षावगमं धर्म्यं सुसुखं कर्तुमव्ययम् ॥ २ ॥
rāja-vidyā rāja-guhyaṁ pavitram idam uttamam pratyakṣāvagamaṁ dharmyaṁ su-sukhaṁ kartum avyayam
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.