A ragi is a musician who sings scripture in the gurdwara, and the office is bound up with the central Sikh practice of devotional singing as a form of worship.
Kirtan
Ragis perform kirtan, the singing of the hymns of the Guru Granth Sahib, ordinarily in a group of three, with a lead singer and a second on harmonium and a player of the tabla drums, and they render the scripture in the musical measures, the ragas, to which much of it was composed, so that the singing follows the musical settings the tradition preserves. Kirtan is not an ornament of Sikh worship but one of its central acts, the hymns of the Gurus sung and heard as a means of devotion and of dwelling on the divine name, so the ragi carries a function at the heart of the gurdwara service.
A recognised skill
The ragi must be skilled both as a musician and in the scripture and its musical tradition, and the office is a recognised and often professional one, ragi groups being attached to gurdwaras or travelling to perform, but it is not a priesthood, since Sikhism has no priestly caste, and its standing rests on skill and devotion. The preservation of the ragas to which the scripture was set is itself a concern of the tradition, and the ragi is the keeper of that musical inheritance. The office reflects the particular Sikh emphasis on sung scripture, and the ragi, singing the words of the Gurus in their appointed measures, occupies a central place in the worship of the community.