The psychology of oneness is a call to the individual to integration within his own being. We are not whole psychologically or physically because we are not in at-one-ment in our inner selves. As we set about becoming integrated or becoming whole, we may first remember that the most important experience for all is to know what is the ideal spiritually.
If, in setting a spiritual ideal, we can guide our motivational potentials toward a singleness of purpose, then we may begin to experience the statement of Jesus that, if your eye be single, the whole body may be full of light. If the eye is single, that is to say, if within ourselves we are single or one in purpose, then physically, mentally, and spiritually we may be filled with light. The principle of oneness is behind the practice of meditation as we seek attunement, atonement, and at-one-ment within. The spirit of oneness requires a spirit of forgiveness because there can be no oneness either within ourselves or in our relationships with others unless we forgive. The spirit of oneness requires that there be a coming together of the forces within ourselves. In this process we may have our own body filled both with light and become a light unto the world.
-The Edgar Cayce Primer: Discovering the Path to Self Transformation