The Guru Granth Sahib does not begin with a narrative or a genealogy. It begins with a numeral and a word: Ik Onkar. One Being. Everything else in Sikh theology is measured against that opening, and the Mul Mantar which follows it is largely a series of refusals as much as a set of affirmations. God is satnam, whose name is truth; karta purakh, the creator; nirbhau, without fear; nirvair, without enmity; akal murat, beyond time; ajuni, not born; saibhang, self-existent; known gurprasad, by the grace of the Guru.
Two of those words do a great deal of work and are easy to pass over. Ajuni, unborn, not subject to birth, is a direct rejection of avatar doctrine. God does not descend, does not take a body, and is not born as anyone; Sikhi does not hold that Ram or Krishna were incarnations of God to be worshipped, and it does not hold that any of the ten Gurus was God either. The Gurus are teachers who transmitted the divine word; Guru Nanak said of himself that he was a servant. Nirankar, without form, rules out images. There is no picture or statue of God in Sikhi, no idol in a gurdwara, and the Sikh Rahit Maryada prohibits idol-worship in terms. What stands in a gurdwara is the scripture, and it is honoured as the Guru, not worshipped as God.
Nirbhau and nirvair are quieter and no less pointed. A being without fear has nothing to defend and can therefore not be placated; a being without enmity has no enemies and can therefore not be enlisted against anyone. Between them they dismantle a great deal of what religion is often used for, and they do it in the first line of the book.