Today you will see the following vaar by Bhai Gurdas jee being sung in gurdwaras -
dIvwlI dI rwiq dIvy bwlIAin] Lamps are lighted in the night of divali festival. qwry jwiq snwiq AMbir BwlIAin] Stars of different variety appear in the sky. PulW dI bwgwiq cuix cuix cwlIAin] In the gardens the flowers are there which are selectively plucked. qIriQ jwqI jwiq nYx inhwlIAin] The pilgrims going to pilgrimage centres are also seen. hir cMdaurI Jwiq vswie aucwlIAin] The imaginary habitats have been seen coming into being and vanishing. gurmuiK suK Pl dwiq sbid smHwlIAin ]6] All these are momentary, but the Gurmukhs with the help of the Word nourish the gift of the pleasure fruit.(6)
The last line says it all ... Bhai sahib is asserting futility of these rituals - whereas our raagis sing as though Guru Sahib (most people dont know its bhai Guradaas to begin with) is encouraging sikhs to light deevas on Deevali......
Jahan Gyan Tahan Dharam Hai | Jahann Jhooth Tahan Paap ||
Also we call it Bandi Chor divas , which is also a myth but thats whole another topic.