I

There are two who enjoy the fruits of their good deeds in the world, having entered into the cave of the heart, seated (there) on the highest summit. The knowers of Brahman call them shadow and light. So also (they are called) by householders who perform five fire- sacrifices or three Nachiketa fire-sacrifices.

Here the two signify the Higher Self and the lower self, dwelling in the innermost cave of the heart. The Seers of Truth, as well as householders who follow the path of rituals and outer forms with the hope of enjoying the fruits of their good deeds, both proclaim that the Higher Self is like a light and the lower self like a shadow. When the Truth shines clearly in the heart of the knower, then he surmounts the apparent duality of his nature and becomes convinced that there is but One, and that all outer manifestations are nothing but reflections or projections of that One.