The yogic sutra tasya vacakah pranavah primarily deals with the most sacred in the Universe - Aum. It is the closest that a mortal can reach towards divinity. The lord signifies Aum himself, he the essence of every work in the universe. If one is successful to understand the significance of this word, he is sure to attain liberation from every material senses.

Tasya Him
Vacakah connoting, denoting, signifying, sign, indicating
Pranavah the sacred syllable Aum

He is represented by the sacred syllable aum, called pranava.

He is distinguished with the sacred syllable aum. He is represented in aum.

Aum is considered the symbol of divinity. It is a sanctified mantra, and needs to be repeated incessantly. Aum is called pranava, which signifies eulogising the divine and accomplishment of divinity.

Sound is vibration, which, as modern science delineates, is at the source of all creation. God is beyond vibration, but vibration, being the subtlest form of His creation, is the nearest one can get to Him in the physical world. So humans consider it as His symbol.

The impersonal essence and source of all being is known as hiranya garbha (golden womb). It is also known as Brahman, who is inside each heart. Aum is the bow and the self is the arrow. With deep concentration, the aspirer has to hit the target, Brahman, so that the individual self and the Universal Soul become one.

Aum is composed of three syllables, a, u, m. The word is written thus - without these three sounds, no words can begin, resound or end in any language. These three sounds are universal; they are the seed (bija) of all words.

The letters a, u, m symbolise speech (vak), mind (manas), and breath of life (prana). As a twig holds leaves together, aum holds all speech together. Aum is the interminable spirit, a symbol of serenity, divinity, stately power, omnipotence and universality.

The three letters of aum represent the three genders, the three gunas, the three aspects of time - past, present and future, and the three gurus - the mother, the father and the preceptor.

They also represent the triad of divinity - Brahma the creator, Vishnu the sustainers, and Siva the destroyer, of the Universe.

Aum as a whole stands for the realisation that releases the human spirit from the restrains of body, mind, intellect and ego. By meditating upon Aum, the sadhaka remains steady, pure and faithful. He transforms into a great soul (mahatma). He finds the presence of the Supreme Spirit within, and earns the peace that is free from fear, dissolution and death.