Bhagavad Gita 9.2

9.2 This is the kingl science, the kingly secret, the supreme purifier, realisable by direct intuitional knowledge, according to righteousness, very easy to perform and imperishable.

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.