Influential monastic author. Originating from Beth Qaṭraye , he was made bp. of Nineveh ( Mosul ) by Cath. Gewargis (661–81), perhaps ca. 676/80. After a short while, however, he left (‘for reasons which only God knows’, as one of the two short biographical accounts puts it) and became a hermit, attached to the Monastery of Rabban Shabur, in the region of Shuster. His writings on monastic spirituality come down in several ‘Parts’, three of which are now known. The First Part, with 82 chapters, evidently circulated widely, and much of it was translated into Greek at the Chalcedonian Monastery of Mar Saba (St. Sabbas), near Jerusalem , in the late 8th or early 9th cent. From Greek, his works were subsequently translated into many other languages, in particular into Slavonic (whence they were included in the Russian edition of the ‘Philokalia’). This Greek translation also included (under Isḥaq’s name) three short works by Yoḥannan of Dalyatha , and an abbreviated form of Philoxenos ’s ‘Letter to Patricius’. The current printed editions of the Greek translation go back to that by N. Theotokis (1770), and have a different chapter numbering from that of the Syriac (a much-needed new edition of the Greek text is in preparation by M. Pirard). A Second Part, consisting of 41 chapters, is preserved complete in a single early ms. The long third chapter of this Part consists of four ‘Centuries’ of short sayings on spiritual knowledge (modelled on Evagrius ’s ‘Kephalaia Gnostica’). A Third Part has also recently come to light, in a ms. in Tehran copied ca. 1900; this contains 17 chapters, two of which are duplicates with the First Part, and one with the Second Part. Though the Second and Third Parts were not translated into Greek, some chapters from them have been identified in Arabic, and they were both evidently known in Syriac monastic circles outside the Ch. of E., as well. The ‘Book of Grace’, probably by Shemʿon d-Ṭaybutheh , has sometimes been wrongly attributed to Isḥaq.
Isḥaq’s monastic spirituality draws on many sources, both Syriac and Greek (in Syriac translation); two authors would appear to have been particularly appreciated by Isḥaq, Yoḥannan Iḥidaya and Evagrius. His teaching lays great emphasis on the immensity of divine love and on the need for humanity to respond to this with wonder and humility.