What is the subtlest education we must acquire, which is core to our lives?

Knowledge can be considered as having two aspects: Baahya Vidya and Brahma Vidya. Baahya Vidya provides the wherewithal for human livelihood. You can study many subjects, earn valuable degrees, acquire lucrative job and manage to spend your life with no worry and fear. This type of Vidya helps you perform whatever job you may doing, be it that of a humble clerk or a prime minister. Brahma Vidya, on the other hand, endows you with the strength, that will enable you to discharge successfully the duty you owe to yourself. It lays down the path which leads both to joy in worldly relations and bliss in the life beyond. Therefore, Brahma Vidya is far superior to all Vidya available to man on earth.