The Guru believes in one God. They believe that all the gurus are the same as Nanak
Set your faces towards unity, and let the radiance of its light shine upon you. Gather ye together, and for the sake of God resolve to root out whatever is the source of contention among you. Then will the effulgence of the world’s great Luminary envelop the whole earth, and its inhabitants become citizens of one city, and the occupants of one and the same throne.
God laughs when two brothers divide their land with a string, saying to each other, ‘This side is mine and that side is yours.’ He laughs and says to Himself, ‘The whole universe belongs to me, but they say they own this portion or that portion.’
For what can be known about God is plain to all, because God is plain to all, because God has shown it to them. Ever since creation of the world His invisible nature, namely His eternal power has been clearly perceived in the things that have been made.

