Theodore was a native of Antioch where he was trained in rhetoric by Libanius before entering the ascetical school led by Diodore (later bishop of Tarsus). He was ordained a priest by Flavian of Antioch in 383 and then in 392 was consecrated bishop of Mopsuestia. In the course of his long episcopal tenure Theodore came to be regarded as one of the foremost theologians and exegetes of the pro-Nicene cause. In addition to numerous biblical commentaries on books of the Old and New Testaments, he produced a set of catechetical homilies explaining the Nicene Creed and the Lord’s Prayer, polemical treatises such as Against Eunomius and Dispute with the Macedonians, as well as other works. Theodore’s On the Incarnation was also polemical, according to the late fifth-century Gennadius of Marseilles:
Theodore, presbyter of the Antiochene church, a man prudent in knowledge and skillful in speech, wrote fifteen books On the Incarnation of the Lord against the Apollinarians and Eunomians, containing as many as fifteen thousand verses, in which he showed by the clearest reasoning and by the testimonies of scripture that just as the Lord Jesus had the fullness of deity, so too he had the fullness of humanity. He taught also that a human being consists only of two substances, that is soul and body, and that mind and spirit are not different substances, but inborn faculties of the soul through which it is inspired and is rational and makes the body capable of sensation. Moreover, the fourteenth book of this work is properly devoted to discussing the uncreated and alone incorporeal and all-ruling nature of the holy Trinity and also the rationality of creatures, which he explains insightfully on the authority of the holy scriptures. But in the fifteenth volume he confirms and strengthens the whole body of his work by citing the traditions of the fathers.1
According to Gennadius, then, Theodore wrote the massive
On the Incarnation before his appointment as bishop while he was still a presbyter; thus his work represents a pro-Nicene Christological outlook of the 380s or early 390s. This was the period in which pro-Nicenes were actively confronting the Christologies of the Apollinarians and Heteroousians (also called Eunomians) as live options, such as was done by Gregory of Nazianzus and Gregory of Nyssa. And herein lies the importance of this work: it is a crucial non-Cappadocian witness to emerging pro-Nicene Christology as it developed in response to the perceived threats of Apollinarius and Eunomius but decades before dyophysite language became problematized through Nestorius. We see in Theodore, then, a Christology that is very much a work-in-progress as he attempts to work out the categories, concepts, and contours with which to articulate his understanding of Christ.