This translation captures the meaning and beauty of the twelve principal Upanishads, omitting a few passages. Original text is not given. An excellent version for the general reader.
Seek ye first the kingdom of God, and everything shall be added unto you. This is the one great duty, this is renunciation. Live for an ideal, and leave no place in the mind for anything else. Let us put forth all our energies to acquire that which never fails--our spiritual perfection. If we have true yearning for realization, we must struggle, and through struggle growth will come. We shall make mistakes, but they may be angels unawares.
-Swami Vivekananda