The Brethren of Purity, the anonymous adepts of a tenth-century esoteric fraternity based in Basra and Baghdad, hold an eminent position in the history of science and philosophy in Islam due to the wide reception and assimilation of their monumental encyclopaedia, the Epistles of the Brethren of Purity. This compendium contains fifty-two epistles offering synoptic accounts of the classical sciences and philosophies of the age; divided into four classificatory parts, it treats themes in mathematics, logic, natural philosophy, psychology, metaphysics, and theology, in addition to didactic fables. Epistle 48 belongs to the fourth part dealing with Divine-Legal matters. It deals specifically with methods that should be employed in advocating for the cause of the fraternity, and in calling different segments of society to join its ranks. The targeted segments include philosophers, kings, Shi'is, and administrators. Special templates for preachers engaging with these particular categories are provided throughout. It also addresses issues of governance and the ideal city, while emphasizing again the primacy of the soul over the body, and the need for followers to know themselves. The Epistle ends with a story based on the famous Bilawhar wa-Budhasaf, given as an illustration of a successful mission. Epistle 48 reveals, more than any other epistle, the political nature of the fraternity and its mission, being, as the editors argue, part of the Fatimid missionary efforts in the period preceding the establishment of the Fatimid Dynasty.