Siri Rag stands at the head of the rag arrangement, and its name says what the tradition thinks of it: the excellent or foremost rag. In the wider Indian repertoire it is an evening measure of grave and deliberate character, unhurried, without the sweetness of the seasonal rags or the urgency of the martial ones, and the hymns collected under it match that temper. They return repeatedly to the shortness of a life arranged around what cannot be kept, and to the plain observation that a person will leave holding nothing.
The section also sets the pattern that the following thirty repeat. The compositions of the Gurus come first, in the order of the succession, and the compositions of the bhagats follow. Within each Guru's portion the forms are grouped, the shorter hymns before the longer, and the whole is closed by the var where the section has one. A reader who learns the shape of Siri Rag knows how to find their way through any section in the volume, which is the practical reason the arrangement is worth understanding rather than merely admiring.
What Siri Rag does not do is introduce anything. There is no preface here, no statement of doctrine, no account of the Gurus. The opening compositions of the Guru Granth Sahib stand before the rag sequence begins and are not part of it, so the first rag section opens in the middle of the matter, with a hymn about the passing of a life, and expects the reader to already be listening.