Ayam atma brahma (Atman is Brahman) — Mandukya Upanishad.
Man’s conception of God and the universe varies with his conception of himself. This is so because with the shift in the centre of his consciousness from the gross to causal bodies, there are corresponding changes in man’s perception of God and the universe. The dynamic equilibrium between the microcosm and the macrocosm at different levels is responsible for these changes in perception.
When man is identified with the gross body (vishwa), the universe appears to him in all its grossness and alluring variety. The corresponding consciousness in the macrocosm is known as virat.
When his subtle body appears more real to him, man lives in the plane of ideas and is not much troubled by the body and its cravings. The universe as it appears to others does not hold much charm for him, for free from body consciousness, he is now in tune with the universal, cosmic Mind. The corresponding macrocosmic consciousness is called hiranyagarbha.
When he is far advanced in spiritual life to the extent of his body and mind becoming unreal to him, man identifies himself with his causal body (prajna) and gets attuned to Personal God, the cause of the universe. The corresponding macrocosmic consciousness is called Ishwara. Man is now said to have realized God in His personal aspect.
On transcending his identity with the causal body and realizing the Atman, the divine core in him, man simultaneously realizes Brahman, the divine core behind the macrocosm. There is now nothing for him to differentiate between microcosm and macrocosm and he realizes the famous Upanishadic equation: Atman = Brahman (Ayam atma brahma. —Mandukya Upanishad).