A striking number of the compositions in the Guru Granth Sahib are built on frames that its audience already knew, and the list is long enough that borrowing has to be understood as a method rather than as an occasional device.
There is the twelve-month poem, of which the volume has two, in different measures and by different Gurus. There is the composition on the lunar days and the one on the days of the week. There is the acrostic on the letters of the alphabet, a form used for teaching children to read, of which the volume has several. There is the ballad of a hero, the wedding song, the funeral lament, the lullaby and the boatman's song. There is the dialogue with ascetics, conducted in the vocabulary the ascetics themselves used.
In every case the shape is familiar and the content is redirected. The audience recognises the form before a word of the teaching has landed, which means no explanation is required and no barrier of unfamiliarity has to be crossed.
The method also carries a claim. A tradition that teaches through an alphabet primer and a calendar poem is addressing people who use alphabet primers and calendar poems, not a class of specialists, and the choice of forms is itself an argument about who religious teaching is for. That argument is made throughout the volume without ever being stated, which is how the Guru Granth Sahib generally prefers to make its arguments.