Majh is one of the sections that makes the Granth's musical scheme regional as well as inherited. It does not belong to the standard pan-Indian classical repertoire in the way that Todi, Bilaval or Sarang do; it is a measure of the Punjab, of the land between the rivers from which the section takes its name, and its presence in a scripture is one of the clearest signs that the Gurus were composing for the people around them rather than for a courtly audience.
The section is substantial, and its best known contents are the twelve-month poem of Guru Arjan, in which each month of the Punjabi year is set against the state of a soul separated from what it loves. The form was not invented for the Granth. Barah maha poems, one stanza to a month, were already a genre of Punjabi and wider north Indian verse, ordinarily secular and ordinarily about a woman waiting for an absent husband. What the Gurus did was take the form intact and change what the waiting is for.
That move is characteristic and it recurs throughout the volume. The Granth rarely invents a genre. It takes a form the audience already knows, the wedding song, the funeral lament, the ballad of a hero, the alphabet primer, the calendar poem, and redirects it. The listener recognises the shape at once, which means the teaching arrives without any need for explanation, and the familiar form does the work that a doctrinal statement would otherwise have to do.