The significance of Pranava mantra is evident from the fact that it is considered one of the faces of Lord Shanmukha.
According to Kachiappa Sivachariar, Lord Siva is seated on the Pranava mantra. It is the foundation of the Vedas, explained Panasai Aruna, in a discourse.
It is said that if a person dies in Kasi, Goddess Parvati puts the dead person on Her lap, and gently strokes the body, while Siva recites ‘Aum Nama Sivaya,' and the soul departs for Kailasa, His abode.
“Aum” is a mantra that will help us cross the ocean of ‘samsara.'
So important is the Pranava mantra that when Lord Brahma says he does not know its meaning, Lord Shanmukha imprisons him.
Lord Brahma says he has the knowledge of the Vedas, but is unable to explain the meaning of the Pranava mantra.
Kachiappa Sivachariar says that if Lord Brahma, the Creator, himself did not know the meaning, how can one believe anyone who claims he has understood the meaning of the mantra? It is not given to everyone to understand its meaning. Only those with gnana understand the mantra.
After imprisoning Lord Brahma, Lord Shanmukha takes on the task of creation. Siva pacifies Shanmukha and points out that Brahma cannot be kept in prison for long and he should be released.
Lord Siva asks Brahma what his sojourn in prison was like. Brahma says he saw the prison as a place for performing penance. Siva then puts Shanmukha on His lap and asks Him the meaning of Pranava. Shanmukha says He will convey it to Siva secretly.
The whole universe is created from “Aum.” Souls are born on this earth, because God wants to release them from bondage. When we take a birth, depending upon the kind of life we lead in this birth, we take further births. And so on the cycle goes, until we become God realised and liberated. So it is to “Aum” that souls owe their liberation.
After the deluge, when God again decides to create, “Aum” is heard. Thus everything has its origin in “Aum.”