In every mantra or stuti, Om is always the first or last word. But why? Firstly, what is Om? OM is the sound of creation and rapid expansion. It is a rhythm and vibration, and the source of all.
A- Brahma
U- Vishnu
M- Mahesh.

Think of this up here☝☝☝....
In the vocalization Om(Aum):
You open your mouth and pronounce Aaaa. That means the sound is created (Brahma)

Then you pronounce Uuuu. The U is always long, and equivalent to (ooooo). That means the sound is sustained or preserved(Vishnu)

After you pronounce Mmmm, while pursing the lips together, then the sound is finished or have ended. (Shiva)

Now let's see Om and the Mantra as a vibration.

Example: Om Namo Narayanaya.

Om - the expanding sound of the universe. (Once you chant it, it means that you're connecting to it)

Namo -I bow.

Narayanaya - Narayan- the source of the universe.

Hence meaning I bow/salute/venerate the source of the universe (*Bhagwan's Name*: Narayan) by starting with the expanding sound of the universe and creation, Om.

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Om Namah Shivaya.

Om

Namah

Shivaya

I bow/salute/venerate the source of the universe (*Bhagwan's Name*) by starting with the expanding sound of the universe and creation, Om.
However it is believed that Lord Shiva is the creator of Om. And Om emerged from him.

Why did Aum become simple Om?

A and U are vowels, that often blend. Like for example in the word auxiliary. So A and U form a soft O, and then there is the M. Hence OM

Ganeshavinayak123
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