Most of us perceive a unified self at the center of our psyche. This perception grows out of our apparently singular and continuous awareness of our own awareness--the experience of hearing an internal voice narrate our perceptions, desires, and memories. The failure of the singularity or continuity of that experience is psychosis. Any number of methods, from psychoanalysis to meditation to prayer, allow the decomposition of that voice into its many component voices, but that won't induce psychosis as long as the audience for those voices remains singular and continuous. If there is any unified element of our self, it's not our will or our judgment, which are formed and informed by disparate impulses and drives. It's our self-awareness, what Freud defined as our consciousness:

What role is left in our account for once-omnipotent consciousness, which hid everything else from sight? No more than that of a sensory organ for perceiving psychical qualities.

That passage, from The Interpretation of Dreams, has always left me wondering about the implied recipient of the perceptions of that organ. It's here that Freud reaches the limits imposed by his strict materialism. At the center of the onion of the psyche, whether it has been peeled by Freudian, Buddhist, or other means, we are left with a mute, inexplicable witness. Can it be explained in materialist terms? Is it our soul? Our pneuma? It's here that Dietrich Bonhoeffer enters this discussion with his exploration of the "natural" ("the form of life preserved by God for the fallen world and directed towards justification, redemption and renewal through Christ"):

...man's "reason" is the organ of knowledge of the natural. Reason is not a divine principle of knowledge and order in man which is raised above the natural, but it is itself a part of this preserved form of life, namely that part which is adapted to the function of introducing into the consciousness, of "perceiving," as a unity whatever is entire and general in the real. Reason, then, is wholly embedded in the natural; it is the conscious perception of the natural as it, in fact, presents itself.

(There's a translator's note that helpfully points out that the German word for "reason" is derived from the German word for "perceive.")

Consciousness is the organ of perception of psychical activity, and reason is the organ of perception of the way of God in this world. That lone unity which Freud finds at the center of our psyche is our only means of witnessing the divine. Freud strongly suggests--and Bonhoeffer (with his belief that grace is a miracle that cannot be earned) seems to concur--that this ineffable component of our selves is mute and passive. Our essential capacity is to be, not to do.