Gregory the Great was pope from 590 to 604. Much of what is known about his papacy comes from the collection of his letters, called the Registrum epistularum, that was assembled after his death. Over 850 of his letters survive, to a vast array of addressees on an equally vast array of subjects. Three are translated here. The first is Letter 1.24, the encyclical letter that Gregory sent in February 591 to the patriarchs of Constantinople, Alexandria, Antioch, and Jerusalem shortly after his elevation to the papacy, as a token of his communion with them. While the bulk of the letter deals with pastoral concerns, its last paragraph (translated below) contains a profession of faith meant to assure his fellow patriarchs of his orthodoxy. Here Gregory confesses his adherence to Nicaea, Constantinople, Ephesus I, Chalcedon, and Constantinople II with its condemnation of the Three Chapters.

Justin hailed from the city of Flavia Neapolis, the modern West Bank city of Nablus, in the Roman province of Syria Palestina. According to his own account in the Dialogue with Trypho the Jew, Justin became a professional philosopher of the Platonist school before adopting Christianity as the true philosophy. From his pen, we have a few surviving works: the First and Second Apologies, which some scholars believe to have been originally a single treatise, probably written in the first half of the 150s, and the Dialogue with Trypho the Jew, written perhaps around 160. He also wrote a refutation of Marcion, which has not survived. Since antiquity, the philosopher Justin who authored these texts has been identified with the Justin who was martyred in Rome, as described in the Acts of Justin. According to that text, Justin was a Christian philosopher who taught in the city of Rome for many years prior to his execution, perhaps in the middle of the 160s.

Opusculum 3 is another work that stems from Maximus’s involvement in the monoenergist and monothelite controversies. It is a fragment of a lost treatise that Maximus wrote On the Activities and the Wills, to Thalassius. Thalassius is most likely the theologian known as “Thalassius the Libyan,” who composed works of ascetic theology, including the Centuries on Theology, now included in the Philokalia. He was a leader of monks in Carthage during the reign of Heraclius (610–641). Maximus wrote several of his most important works in response to Thalassius, including his massive Questions on Sacred Scripture (ca. 633), in which he expounds on sixty-five difficult passages in scripture that Thalassius had identified. Maximus wrote On Activities and Wills in the early 640s, once he had fully entered the monothelite controversy. Only a few fragments of this treatise survive: chapter 50 (as Opusculum 2), chapter 51 (the present Opusculum 3), and some quotations in the florilegium known as Opusculum 26b.

In the late 410s or early 420s, in an epistle that is no longer extant, a monk in Gaul named Leporius, motivated by a desire to avoid attributing change and the human condition to God in the incarnation, wrote that he was disinclined to confess that God was born of a woman. Instead, he preferred to say that a perfect human being was born along with God rather than as God. The epistle sought to demonstrate this basic point and related Christological consequences through the interpretation of several key passages of scripture. But the form of Christological dualism that he advocated soon came to be deemed aberrant. When he refused to recant his views, Proculus, bishop of Marseilles, and Cillenius, a bishop of an unknown see in southern Gaul, formally rebuked Leporius in circumstances that remain unclear, and expelled him from Gaul. Along with two disciples named Domninus and Bonus, he took refuge in North Africa with Augustine.

Theodoret was born ca. 393 in Antioch to a prominent Christian family. As the only child of a devout mother, he was not only well educated in the classical sense but was also exposed to monastic spirituality and piety from an early age. While still a child he was ordained a reader in the church of Antioch. Later he moved to a monastery near Apamea (Syria Secunda), where he became a professed monk. At the age of thirty, around 423, he was elected bishop of Cyrrhus.

The long-lived Narsai – he died a nonagenarian ca. 500 – was a poet and teacher at both the School of Edessa and the School of Nisibis. His thought and works were foundational for the development of theology in the Church of the East. Steeped in Syriac literary traditions, principally the writings of Ephrem the Syrian, Narsai was also among the first generation of Syriac authors to be shaped by the theology and interpretative strategies of Theodore of Mopsuestia (d. 428) through translations of the Greek into Syriac. The work of translating Theodore’s works was centered at the School of Edessa and coincided with the fateful events around the Council of Chalcedon and the resulting strife surrounding the Christological debates. Narsai’s poetry displays his dynamic reception of both Ephrem and Theodore’s theological and interpretative programs. Working in the aftermath of Council of Ephesus, Narsai became embroiled in the Christological controversies, often reflected in his poetry. At an uncertain date prior to the closure of the School of Edessa in 489, Narsai and his colleagues departed from Edessa, leading to the formation of the School of Nisibis within the Persian Empire.

Tertullian wrote Against Praxeas in the early 210s. It is thus a product of the latest part of his career, when he had become a vocal supporter of what he called the New Prophecy. This was a controversial, revivalist movement, termed Montanism by its opponents, which owed its origins to the region of Phrygia in Asia Minor. There, in the late 150s, a new convert to Christianity named Montanus began making prophecies about the coming end of days, and the consequent need for Christians to follow a more rigorous code of behavior. Other prophets followed him, including two women named Prisca and Maximilla. As Against Praxeas makes clear, the followers of Montanus placed great significance on the Paraclete (“Advocate” or “Helper” in Greek), who is identified with the Holy Spirit in the Gospel of John (see especially 14:26). Tertullian says that the Paraclete had provided him with new insight into the relation between God and Christ, thus suggesting that his account of the Father and Son was closely linked with the New Prophecy of Montanism, which was subsequently dismissed as heretical.

In what follows, the fifth-century Syriac writer Narsai considers several moments from biblical stories in order to understand their significance for how Christians should think about Christ. Each of the vignettes Narsai discusses – the creation of humanity, an angel’s visit to Mary to announce her pregnancy, Jesus’s circumcision, and his baptism by John – offers a way to consider the purpose and nature of Christ as the Word of God. Throughout Narsai affirms the immutability of the Word even in the incarnation and stresses that it was the human being who was the subject of these biblical events, not the immutable Word of God. Narsai holds that the immutable Word did not literally became flesh in the incarnation (since that would be impossible for the Word), but rather indwelt the human being for the purpose of revealing knowledge of God. Narsai’s ideas about these situations and others frequently reflect the teachings of Theodore of Mopsuestia, a writer and church leader who died in 428 and whom Narsai revered. That said, his ideas also go beyond Theodore’s teachings, and show us the development of Christian thought about Christ from one generation to another.

The motivations behind Apollinarius of Laodicea’s Christology are debated by scholars, but it is safe to say that from the beginning he opposed any sort of dualist Christology.1 In Antioch, in whose ecclesiastical affairs Apollinarius was involved since the early 360s, two presbyters connected with the pro-Nicene Meletian faction, Diodore and Flavian, espoused a dyophysite Christology.2 Diodore became bishop of Tarsus in 378 and Flavian bishop of Antioch in 381. It seems that it was not until the late 370s that Apollinarius came into conflict with them, over issues that were as much as ecclesio-political as Christological. Fragments of Apollinarius’s writings against Diodore and Flavian are preserved in three later polemical treatises: Theodoret of Cyrrhus’s Eranistes, Leontius of Byzantium’s Adversus Fraudes Apollinaristarum, and the Doctrina Patrum de Incarnatione Verbi. These treatises mention a number of different Apollinarian sources for the fragments they preserve, but it is unclear if they refer to a single tract by Apollinarius or several. At least one of Apollinarius’s writings against Diodore was addressed to a certain Herakleion who is otherwise unknown (Fragments 117–120). No more than titles are known about the others, however many there were.

Gregory the Great was the Roman pontiff from 590 until his death in 604. In the mid-570s he abandoned a successful career in government in order to become a monk. In 579 or 580 Pope Pelagius II ordained him a deacon and sent him to Constantinople as the papal ambassador. He spent about six years in the imperial capital, where he became the center of a circle of monks and clerics who read the scriptures together. The lectures on the biblical book of Job that he delivered in this setting he later revised for publication as the Moralia in Job, his most famous work and a treasure-house of moral, spiritual, and theological insight. Upon his return to Rome he resumed his monastic life, but was elected pope after the death of Pelagius II in 590.

The date of this text written by Apollinarius of Laodicea (ca. 315–392) is difficult to determine with specificity.1 It should simply be placed in the late 360s or 370s. Here Apollinarius lays out his understanding of the communicatio idiomatum, a Latin phrase that refers to the transference of traits in the incarnate Christ. As Apollinarius presents it here, the communicatio idiomatum permits a theologian to both observe and speak of the divinity sharing in the body’s characteristics and the body sharing in the divinity’s characteristics with respect to the incarnate Christ. Apollinarius notes that the conjunction of the two natures in Christ (see 4 below) results in a single, fundamental, undivided, and indivisible union between what is “same-in-substance” with God and what is “same-in-substance” with humanity. This “double consubstantiality,” as it is called – that is, Christ is homoousios with God and homoousios with humanity – is the Christological mechanism, so to speak, that allows for each nature to share in the qualities of the other without the philosophical or theological implications of sharing.

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: