Almost 100 sermons and 150 letters of Leo I have been preserved.
Tome At the
Second Council of Ephesus in 449, Leo's representatives delivered his famous
Tome, a statement of the faith of the Roman Church in the form of a letter addressed to
Archbishop Flavian of Constantinople, which repeats, in close adherence to
Augustine of Hippo, the formulas of western
Christology. The council did not read the letter nor did it pay any attention to the protests of Leo's legates but deposed Flavian and
Eusebius of Dorylaeum, who appealed to Rome. That is one reason that the council was never recognized as ecumenical and was later repudiated by the Council of Chalcedon. It was presented again at the subsequent Council of Chalcedon as offering a solution to the Christological controversies still raging between East and West.
Council of Chalcedon Eutyches, in the beginning of the conflict, appealed to Leo and took refuge with him on his condemnation by
Flavian, but on receiving full information from Flavian, Leo took his side decisively. Leo demanded of the emperor that an
ecumenical council should be held in Italy, and in the meantime, at a Roman synod in October 449 (Source needed), repudiated all the decisions of the "
Robber Synod". In his letters to the emperor and others he demanded the deposition of Eutyches as a
Manichaean and
Docetic heretic. The
Council of Chalcedon of 451 rejected the heresy of Eutyches who denied the true human nature of the Son of God, and affirmed the union in his one Person, without confusion and without separation, of his two natures, human and divine. The acts of the council report: "After the reading of the foregoing epistle, the most reverend bishops cried out: This is the faith of the fathers, this is the faith of the Apostles. So we all believe, thus the orthodox believe. Anathema to him who does not thus believe. Peter has spoken thus through Leo. So taught the Apostles. Piously and truly did Leo teach, so taught Cyril. Everlasting be the memory of Cyril. Leo and Cyril taught the same thing, anathema to him who does not so believe. This is the true faith. Those of us who are orthodox thus believe. This is the faith of the fathers. Why were not these things read at Ephesus? These are the things
Dioscorus hid away." Leo firmly declined to confirm their disciplinary arrangements, which seemed to allow Constantinople a practically equal authority with Rome and regarded the civil importance of a city as a determining factor in its ecclesiastical position; but he strongly supported its dogmatic decrees, especially when, after the accession of Emperor
Leo I (457), there seemed to be a disposition toward compromise with the Eutychians.
Teaching on Christ (11th century) Leo's writings (sermons and letters) mostly discuss theological questions concerning the person of
Jesus Christ (Christology) and his role as mediator and savior (Soteriology), which is partially connected to the Council of Chalcedon, in which Roman legates represented Leo. Subsequently, through numerous letters to bishops and members of the imperial family, Leo incessantly worked for the propagation and universal reception of the faith in Christ as defined by Chalcedon, also in the eastern part of the Roman empire. Leo defends both the true divinity and true humanity of Christ against heretical one-sidedness. He takes up this topic also in many of his sermons, and over the years, he further develops his own original concepts. A central idea around which Leo deepens and explains his theology is Christ's presence in the Church, more specifically in the teaching and preaching of the faith (Scripture, Tradition and their interpretation), in the liturgy (sacraments and celebrations), in the life of the individual believer and of the organized Church, especially in a council. To Leo the Great, Mariology is determined by
Christology. If Christ were divine only, everything about him would be divine. Only his divinity would have been crucified, buried and resurrected. Mary would only be the mother of God, and Christians would have no hope for their own resurrection. The nucleus of Christianity would be destroyed. The most unusual beginning of a truly human life through her was to give birth to Jesus, the Lord and Son of King David.
Oriental Orthodox view Leo's Christological formula however was not entirely well received. Following the death of Dioscorus, the
See of Alexandria split into two rival patriarchates; opposing and supporting Chalcedon respectively. The former of which, led by
Timothy II of Alexandria would condemn both the heresy of Eutyches as well as the Council of Chalcedon and the Tome of Leo at the
Third Council of Ephesus. The communion that accepted Ephesus III is known today as the
Oriental Orthodox Church. Ephesus III accused Leo's formula of two natures after the union as being fundamentally no different to the view of Nestorius, contradicting Cyril of Alexandria's formula of "mia physis tou Theo logou sesarkōmenē", or "one (mia) nature of the Word of God incarnate" (μία φύσις τοῦ θεοῦ λόγου σεσαρκωμένη). Several Oriental Orthodox Church historians, such as Pakhoum A. El-Moharraky and Waheeb Atalla Girgis have viewed the council as a dispute with the Church of Rome over precedence among the various patriarchal sees. Coptic sources, both in Coptic and in Arabic, suggest that questions of political and ecclesiastical authority exaggerated differences between the two professions of faith. The Coptic Orthodox Christians are Miaphysites, which means they believe that Jesus Christ is both 100% human and 100% divine but in one person without mingling, confusion or alteration. In every liturgy till this day, the Copts recite “Christ's divinity parted not from His humanity, not for a single moment nor a twinkling of an eye".
Heir of Peter Leo assumed the papacy at a time of increasing barbarian invasions; this, coupled with the decreasing imperial authority in the West, forced the Bishop of Rome to take a more active part in civil and political affairs. He was one of the first bishops of Rome to promote papal primacy based on succession from
Peter the Apostle; and he did so as a means of maintaining unity among the churches. Besides recourse to biblical language, Leo also described his own special relationship with Peter in terms derived from Roman law. He called himself the (unworthy) heir and deputy (
vicarius) of Peter, having received his apostolic authority and being obliged to follow his example. On the one hand, Peter stood before him with a claim on how Leo was to exercise his office; on the other hand, Leo, as the Roman bishop, represented the Apostle, whose authority he held. Christ, however, always comes out as the source of all grace and authority, and Leo is responsible to him for how he fulfilled his duties (sermon 1). Thus, the office of the Roman bishop was grounded on the special relationship between Christ and Peter, a relationship that cannot be repeated per se; therefore, Leo depended on Peter's mediation, his assistance and his example in order to be able to adequately fulfill his role and exercise his authority as the Bishop of Rome, both in the city and beyond. == Leo and Attila ==