Japji Sahib stands at the head of the Guru Granth Sahib and is recited by observant Sikhs each morning. It is Nanak's, composed within his lifetime, and it functions as a summary of his teaching in a way that few founding texts manage.
It opens with the foundational statement of the divine nature, one being, truth by name, creator, without fear, without enmity, timeless, unborn, self-existent, known by grace, and then proceeds through thirty-eight stanzas and a closing verse.
Its structure is an argument. It asks in the first stanza how one becomes truthful and how the wall of falsehood is broken, and answers: by walking in the divine order, hukam. It then works through and dismisses the standard means, ritual purity, silence, accumulation of wealth, cleverness, and returns repeatedly to the same answer.
The middle stanzas set out five stages or realms, from the realm of duty through knowledge, effort and grace to truth, and the description becomes deliberately vast: countless worlds, countless forms of creation, and an insistence that the extent cannot be stated. Nanak's cosmology is not a small one, and the passage rejecting the idea of a single world and a single heaven is striking for its period.
The final verse uses the image of a smith's workshop, self-control the furnace, patience the smith, knowledge the anvil, and describes the divine word being struck in it.
It is meant to be understood, not merely recited, and Sikh teaching says so directly.