Here are excerpts from a lecture by Yogi Bhajan on April 8, 1971:

The Mantra EK ONG KAR SAT NAM SIRI WHA GURU, has 8 vibrations and describes the Glory of the Infinite. In the time period 2 and 1/2 hours before the rising of the Sun when the channels are most clear, if the Mantra is chanted in sweet harmony, you will become one with the One. It opens the solar plexus, which in turn charges the solar centers and connects them with the Cosmic Energy. All mantras are good, they are all for the awakening of the Divine but this Mantra is effective and it is the mantra for this time. It is a key which has eight levers and this key can open the lock of the time which is shaped in the form of an 8 (wheel over wheel). Therefore, when this Mantra is sung while applying the neck lock, at the point where Prana and Apana meet Sushumana, the vibration opens the cosmic lock. In the town of Goindwal in Punjab, India, even today this Divine Mantra is still inscribed on the walls of the Baoli Sahib (sacred well) at the house of Guru Amar Das, the Guru of Guru Ram Das, through whose blessing today we vibrate in the Divine ecstasy. I disclose to you today this secret of the Divine for the uplift of humanity and those who will follow it will be liberated and be one with the Divine.” ~ Yogi Bhajan

Chant this mantra with Snatam Kaur:

 

Here is a video of Guruka Singh describing this meditation: