The Denkard was compiled two centuries after the Arab conquest of Iran, in the Abbasid world where Zoroastrianism, once the imperial religion of the Sasanians, was becoming the faith of a shrinking, taxed and disputing-with-its-neighbours minority. The work's temper reflects that setting. Book three, the largest surviving portion, is a long sequence of doctrinal and apologetic chapters, defending the coherence of the good religion in the vocabulary of reasoned argument, treating the nature of the two principles, the goodness of the creator, the purpose of creation and the resurrection, and answering, sometimes explicitly, the objections of Muslims, Christians, Jews and sceptics.
Book four gathers traditions about the transmission of the sacred learning, including the celebrated account of how the Avesta was assembled, scattered by Alexander, and recollected under the Sasanian kings, a narrative that shaped all later understanding of the canon's history. Book five answers questions put by inquirers, book six is a vast anthology of andarz, the gnomic wisdom literature of the sages, and book seven narrates the life and marvels of Zarathustra from his pre-existence to his mission. Books eight and nine perform the service scholars prize most: chapter-by-chapter summaries of the twenty one nasks, the divisions of the Sasanian Avesta, and detailed exposition of three of them. Since most of that Avesta never survived the following centuries, the Denkard's digest is the principal window onto what was lost.