Ayam Atma Brahma - This Self is Brahman
The individual Self is identical with the cosmic principle.
Ayam Atma Brahma points to the immediate experience of self and declares it to be Brahman. What we truly are, beneath all appearances, is the infinite absolute.
This Self is Brahman.
The fourth mahavakya completes the teaching of non-dual identity.
Mandukya Upanishad