Zoroastrian theology orders the world into creations, and each order has its ratu, its lord, exemplar and guardian: the best of each kind, through which the kind is addressed. The Visperad is the liturgy of all of them together. Its twenty-four sections, the kardas, are woven into the fabric of the Yasna at fixed points, so that the celebrating priests move through the familiar central service while repeatedly opening it out into invocations of the whole hierarchy of spiritual and material excellence, the lords of the years and seasons, of the festivals themselves, of the categories of the righteous, of the Gathic hymns understood as beings worthy of worship. Nothing new happens at the ritual table; what changes is the reach of the address.
Scholars of Iranian religion read the service as a precious survival of the archaic Indo-Iranian instinct to worship through exemplars, the same instinct that in the Vedic world produced the invocation of the foremost of each class, here systematised by the Zoroastrian priesthood into a fixed liturgical expansion. For the celebrating pair of priests, the zot and his assistant the raspi, the Visperad is a heavier undertaking than the daily Yasna, longer in text and stricter in its preparation, and its performance has always been the mark of the fully trained liturgical priest. The service is one of the clearest demonstrations that Zoroastrian worship is not petition but the ritual maintenance of the good creation, order answered with order.