theologian-monk of a monastery at Rhaithu, a port on the Sinai Peninsula, considered the last of the Neo-Chalcedonian authors. His writings sought an orthodox formulation of doctrine on the nature of Christ. He thereby proposed to integrate the authoritative expression of Christ's coexisting human and divine essences as decreed by the Council of Chalcedon (451) with the widespread mystical variants popular among the Eastern monks and other proponents of monophysitism, a doctrine emphasizing the divine element in Christ to the derogation of his humanity.

Theodore's principal work, written between 580 and 620, was the Proparaskeuē (“The Preparation,” or “Basic Indoctrination”), in which he attempted to justify some of the more contemplative Christological terminology of the eminent 5th-century orthodox theologian Cyril of Alexandria. By exposing the doctrinal deviations in the extreme theological positions of his time, viz., the concept of Christ as predominantly divine or human, advocated respectively by the monophysite or Nestorian schools, Theodore intended to show the middle ground of orthodox teaching. He also rejected the important early 6th-century attempt by the scholarly Severus of Antioch to achieve a doctrinal consensus but with a monophysitic orientation.

Of possible authenticity is the Aristotelian Compendium of Logic and a tract “On Sects” attributed to Theodore. He is currently thought to be identical with the semi-monophysite Theodore, bishop of Pharan, who is credited by some manuscripts with the Compendium of Logic. The critical and complete text of “The Preparation” was published by Franz Diekamp (1938).