ऋतं पिवन्तौ सुकृतस्य लोके गुहां प्रविष्टौ परमे परार्धे ।छायातपौ ब्रह्मविदो वदन्ति पञ्चाग्नयो ये च त्रिणाचिकेताः ॥ १ ॥
In plain words
Two [selves], drinking the fruit of good deeds, have entered the cave [of the heart] in the supreme farther region [of the body]. Knowers of Brahman speak of them as shadow and sunlight -- and so do those who maintain the five sacred fires, and those who have kindled the Nāciketa fire three times.