Solstice Sadhanas give us the opportunity to recite Japji together. Japji Sahib is Guru Nanak's description of his own enlightenment experience as a realized yogi.
"[Guru Nanak] was a yogi and he had the jal samaadhee. Jal samaadhee means he went under the water and came out after three days. When he came out, he uttered the words Sat Naam and after that he uttered Japji."
Here is the story:
One morning, while taking his bath before his meditation, Guru Nanak immersed himself in the water and did not resurface for three days. His breath became so still and so deep that he could sustain himself under the water. During those three days, he had his enlightenment experience. He saw the Cosmic play of Divine Consciousness, and the role and purpose of human life within it.
After having this vision, Guru Nanak recorded his experiences in Japji Sahib, The Song of the Soul. Japji Sahib is Guru Nanak's description of his own enlightenment experience as a realized yogi. But the gift of Japji is the power of the Shabad Guru, the teacher who manifests through the Sound Current. When Guru Nanak recited Japji Sahib, he brought a new spiritual technology to humanity.
[Excerpt from Guru Nanak and the Yogis]
Enjoy this video of Yogi Bhajan speaking all about Guru Nanak and Japji, with creative narrative and visuals by Harimander Singh.
Japji Sahib: Guru Nanak & The Kali Bein (The Black River)