Bhagavad Gita 9.2

राजविद्या राजगुह्यं पवित्रमिदमुत्तम् |
प्रत्यक्षावगमं धर्म्यं सुसुखं कर्तुमव्ययम्

Translation

This knowledge is the king of sciences and the most profound of all secrets. It purifies those who hear it. It is directly realizable, in accordance with dharma, easy to practice, and everlasting in effect.