“​The gong is the sound of creation. All sounds and all words have come from it. It is the nucleus of all words. It is the multiple, projective sound to put you through. It is not a drum or a musical instrument. It is God. It is reinforced vibration. It is like a million strings vibrating at once. Only instrument in which you can create the space vibrations - where you can become weightless and soundless and go through it.” 
– Yogi Bhajan

The gong is the spirit song 

The gong also has an effect on the mind. The sound waves help to open the subconscious mind to a meditative state. The mind naturally releases with the gong.
It takes only 3 to 90 seconds for the gong to have an affect on the mind.
Then we have the opportunity to expand our own psyche to new aspects of our selves and the world around us.
'The Gong is the spirit song.
The primal whisper of the soul.
Its sound is the echo of the Original Word that created the world,
the sound within all sounds.
Listen with outer and inner ears.
Feel its pulsations and let the millions of vibrations
dance and flow through your senses.
You will become fearless, relaxed and awakened.
The ancients sought this experience on the tops of mountains and
at the sacred places.
The voice of God would thunder in spectacular strokes of lightning.
The clap of thunder -  stopped all thought, stripped away pretence,
shook loose the deepest fears,
and rejuvenated the nervous system.
It created strength, peace and healing.
The gong is that sound. It is the flash of inner light.
The mallet is the will of the Infinite, the gong the creation,
and the sound is the spirit song, the heartbeat of the soul.'
Yogi Bhajan