Three major bodies of writing in Syriac survive from fourth century: Aphrahat's twenty-three Demonstrations, Ephrem's extensive writings in both prose and poetry, and the anonymous guide to the spiritual life entitled The Book of Steps. The most important figure of early Syriac literature is the theologian poet Ephrem, most of whose life was spent as a deacon serving the church in Nisibis. Ephrem's prose works fall into three categories, the Prose Refutations, the commentaries, and works written in artistic prose. A number of biblical commentaries have a strong claim either to be by Ephrem himself, or to represent his teaching or that of his immediate followers. These include two Old Testament commentaries, on Genesis and on Exodus, which are of particular interest for the many parallels with Jewish exegetical tradition. The fifth century was to witness a major change in the character of Syriac literature, as it came more and more under the influence of the Greek-speaking world.