OM. This eternal word is all: what was, what is, and what shall be, and what beyond is in eternity. All is OM.
Brahman is all and Atman is Brahman.
Atman, the Self, has four conditions.
The first condition is the waking life of outward-moving consciousness, enjoying the seven outer gross elements.
The second condition is the dreaming life of inner-moving consciousness, enjoying the seven subtle inner elements in its own light and solitude.
The third condition is the sleeping life of silent consciousness when a person has no desires and beholds no dreams. That condition of deep sleep is one of oneness, a mass of silent consciousness made of peace and enjoying peace.
The fourth condition is Atman in its own pure state: the awakened life of Pure Consciousness. It is neither outer nor inner consciousness, nor semi-consciousness, nor sleeping consciousness, neither consciousness nor unconsciousness. It is Atman, the Spirit itself, that cannot be seen or touched, that is above all distinction, beyond thought and ineffable. In the Union with it is the supreme proof of ones reality. It is the end of evolution and non-duality. It is peace and love.
This Atman is the eternal word OM.
Its three sounds A, U and M are the first three states of consciousness...
The first sound A is the sound of waking consciousness, common to all men...who knows this attains in truth all his desires, and in all things becomes first.
The second sound U is the second state of dreaming consciousness...who knows this raises the tradition of knowledge and attains equilibrium.
The third sound M is the third state of sleeping consciousness..who knows this measures all with his mind and attains the final End.
The word OM as one sound is the fourth state of Supreme Consciousness. It is beyond the senses and is the end of evolution. It is non-duality and love.
He goes with his self to the Supreme Self who knows this, who knows this.
(ADDED NOTE ON OM : Om and Amen are one. Also Amun, Amin, Alahim, Alm )