The expression of that (Ishwara) is the Pranavah (OM)
The expression of the Word as God (Ishwara) is both universal and transcultural. Just as an idea/a concept is formulated by language which is composed of words which originates first in the mind and then communicated either vocally or in symbol form called writing, likewise both expression of Consciousness and manifestation (such as the universe) starts in the Mind of God (Ishwara) and is communicated as an (internal/external) expression through the Word, being OM in Sanskrit. Sometimes that original vibration (Pranava) known as OM is alluded to stand for the Original Mind.
The vocal aspect of communication that manifests the Universe, the original parcels of power vibrations are called the Matrikas (or ‘little mothers’, i.e. giving birth to the universe and its phenomena). This is where Mantras originate from.
The interactions of those Matrikas form into a structural language that translates as a geometrical arrangement of energy patterns that provide the foundation of the visible universe as we know it. That particular science is known as Yantra. Therefore Mantras are the universal vibrations that give rise to cosmic energetic patterns known as Yantras (which in turn manifest the world of name and form).
The Manduka Upanishad discusses OM as a four-fold syllable: A+U+M+Silence. For example AUM represents past, present, future and that which transcends time.
AUM is representative of the four states of the self: seeking the physical, seeking inner thoughts, seeking the causes and realizing oneness with the Self Within.
AUM expresses the four states of consciousness: waking, dreaming, deep sleep and turiya or the undifferentiated state of consciousness when one is united with the Self Within.
OM is the expression of God (Ishwara) as OMnipotent, OMnipresent, OMniscient and OMnifarious as It expresses Itself inherently in the Universe.