The song is a prayer that behaves like a love song, which is exactly the tradition it comes from. Kun faya kun is the phrase of creation from Surah Ya-Sin, be and it is, and the song uses it as a refrain the way a qawwali uses a name: repeated until it stops being a quotation and becomes a state. The second line that carries the same weight is karam karein, data karam karein: may the giver keep giving. The whole song is those two requests, ornamented.
The verse that made the song famous is the song's entire theology in one line. Jab kahin pe kuchh nahin, bhi nahin tha, wahi tha. When there was nothing anywhere, nothing at all, He was there. It is the oldest claim in monotheism, and the song delivers it with the wonder of someone discovering it fresh: wahi tha, wahi tha, He was there, He was there. The second verse extends it: whatever is inside me, whatever is inside you, maula wahi, the Master is the same. The unity of everything is stated as a discovery.
Then the song turns to the image of the dyer. Rangreza is the one who dyes cloth, and in the Sufi poetry of the region it is one of the great titles for God: the world is cloth, and we are being dyed. Rang mera, tann mera, mann: dye my colour, my body, my mind. The next verse pairs the two weathers of the soul: sajra savera, a dry, scorched morning, and kajra andhera, the kohl-dark night, lit by your burning flame. And then the turn of the whole song: qatra mila jo tere dar barse, when a drop fell and rained at your door. The drop is the pilgrim, and the door is the shrine, and the song has reached its geography at last.
The last two verses are the song's real prayer. Mujhpe karam sarkar tera: your grace on me, master. Karde mujhe mujhse hi riha: set me free from myself. It is the sharpest prayer of the decade, because it locates the prison correctly: the thing I need rescuing from is me. The verse that follows explains why he needs it. Main toh jag ko na bhaaya, tune gale se lagaya. The world did not like me, and you pulled me to your chest. It is the theology of the outcast, and it is why the song belongs to everyone who has ever been unwanted.
A.R. Rahman sang it with Javed Ali and Mohit Chauhan at the shrine of Nizamuddin Auliya in the film, and the song's own address, ya Nizamuddin sarkar, comes from the same geography. The recording people mean is the one from the film, and the version on T-Series is the one that has travelled.