Shabad, the Word, is in Sikh teaching the divine utterance through which God is known and by which a person is transformed. In ordinary usage it is also the name for an individual hymn of the Guru Granth Sahib, and the two senses are deliberately joined: the compositions are held to be the divine Word, and the tradition's statement is that the Guru is the shabad and the shabad is the Guru.
That identification is what makes the Sikh scripture a Guru rather than a record of what Gurus taught. Guru Nanak's own compositions locate the Guru in the Word rather than in a person, in the Siddh Gosht, his recorded dialogue with the Nath yogis, he says that the shabad is his Guru, so that the vesting of guruship in the scripture in 1708 is presented within the tradition as the completion of something present from the beginning rather than as an innovation forced by the end of the line.
The Word is encountered principally through kirtan, the singing of the hymns, which is the central Sikh act of worship. The Guru Granth Sahib is arranged by raga, musical mode, rather than by author or subject, thirty-one principal ragas, with the compositions of all the contributing Gurus and saints grouped within each, and that arrangement is itself a statement that the text is meant to be sung rather than merely read. Listening, sunia, is treated at length in Japji Sahib as itself transformative, and the tradition holds that congregational kirtan works on the hearer directly.
The scripture's contents are notably plural. Alongside the compositions of six Gurus it includes the work of fifteen bhagats, Hindu and Muslim saints of varied region and social background, among them Kabir the weaver, Namdev the calico-printer, Ravidas the leatherworker, and the Sufi Farid, together with bards and others. That such compositions stand within a text which is itself the Guru is the strongest available statement of the tradition's position that the divine Word is not the property of any one community, and it is regularly cited in exactly that connection, including in arguments against caste.