Know Thyself
"Know thyself" was, of course, one of the cardinal principles in the philosophy of Socrates and his chronicler Plato, an early and emphatic assertion of the importance of self knowledge in the development of the good life.

In the essay "From East to West" in Romanticism Comes of Age, Barfield offers his own reading of its significance for the evolution of consciousness:

In the Greek expression or "Know thyself!" we really find the same principle [as the Buddhist conception of Tat Tvam Asi] embodied. This was no exhortation to introspection, but rather, in modern jargon, an exhortation to make the unconscious conscious. If "I" in my true self--that is, if you choose, in my unconscious self--am that (the apparently objective), then it is only by knowing that and by knowing it imaginatively that I can "know myself." (30-31)

See in particular "From East to West" (RCA 25-46).