All longing to know the oneness in existence is yoga. 
The word yogi, means one who has realized oneness of existence.

Yoga is the science and technology to know the essential nature of how this life is created and how it can be taken to its ultimate possibility.

Sadhguru

The power of mantra

Today modern science is proving to us beyond any doubt, that the whole existence is just a vibration of energies. Where there is a vibration there is bound to be a sound. So, in yoga we say the whole existence is sound or sound is God. Which is known as Nada Brahma, which means that all is brought into being by frequency, by sound. Sound provides the pattern and the motion by which all forms arise and Creation is then a complex amalgamation of sounds. Among these complex web of sounds, there are a few sounds which are key sounds. These key sounds are referred to as mantras. A mantra can open up a completely different dimension of existence for a human being. And to know and experience this divinity, means evolving our energies to higher possibilities, evolving our energies to subtler dimensions within ourselves. And this we can do with sound.