He who knows at the same time both Vidya and Avidya, crosses over death by Avidya and attains immortality through Vidya.
Those who follow or "worship" the path of selfishness and pleasure (Avidya), without knowing anything higher, necessarily fall into darkness; but those who worship or cherish Vidya (knowledge) for mere intellectual pride and satisfaction, fall into greater darkness, because the opportunity which they misuse is greater.
In the subsequent verses Vidya and Avidya are used in something the same sense as "faith" and "works" in the Christian Bible; neither alone can lead to the ultimate goal, but when taken together they carry one to the Highest. Work done with unselfish motive purifies the mind and enables man to perceive his undying nature. From this he gains inevitably a knowledge of God, because the Soul and God are one and inseparable; and when he knows himself to be one with the Supreme and Indestructible Whole, he realizes his immortality.
XII
They fall into blind darkness who worship the Unmanifested and they fall into greater darkness who worship the manifested.
XIII
By the worship of the Unmanifested one end is attained; by the worship of the manifested, another. Thus we have heard from the wise men who taught us this.
XIV
He who knows at the same time both the Unmanifested (the cause of manifestation) and the destructible or manifested, he crosses over death through knowledge of the destructible and attains immortality through knowledge of the First Cause (Unmanifested).
This particular Upanishad deals chiefly with the Invisible Cause and the visible manifestation, and the whole trend of its teaching is to show that they are one and the same, one being the outcome of the other hence no perfect knowledge is possible without simultaneous comprehension of both. The wise men declare that he who worships in a one-sided way, whether the visible or the invisible, does not reach the highest goal. Only he who has a co-ordinated understanding of both the visible and the invisible, of matter and spirit, of activity and that which is behind activity, conquers Nature and thus overcomes death. By work, by making the mind steady and by following the prescribed rules given in the Scriptures, a man gains wisdom. By the light of that wisdom he is able to perceive the Invisible Cause in all visible forms. Therefore the wise man sees Him in every manifested form. They who have a true conception of God are never separated from Him. They exist in Him and He in them.