THE history of the Christian Church is marked by schism and split. Western Christendom was divided by the Reformation. Much earlier, the formal excommunications of 1054, and the sacking of Constantinople by the soldiers of the Fourth Crusade in 1202, left their marks engraved on the fault-lines of Europe.

Earlier still, the Council of Chalcedon of 451 meant that those Christian communities and Churches on the fringes of the Byzantine Empire - the Syrians, Copts, Armenians, Ethiopians, and the Malankara Christians of South-West India - were left outside the larger (Greek and Latin) part of Christendom, which accepted the Council's decrees.

This is the most ancient, significant division in the Christian Church, and at its centre is and was nothing less than the nature of Jesus Christ.

It was therefore a historic moment when, at a meeting in Cairo in October, an Agreed Statement on Christology was signed by Metropolitan Bishoy of Damietta of the Coptic Orthodox Church, and me, as the co-chairs of the International Dialogue between the Anglican Communion and the Oriental Orthodox Churches, set up by the Lambeth Conference of 1998.

Anglicans at the Reformation inherited the Chalcedonian Christology from the Western Catholic Church. Yet significant Anglican theologians, such as Richard Hooker and Richard Field, recognised the significance of St Cyril's understanding of the person of Christ, which is definitive for the Oriental Orthodox Churches.

Cyril speaks of the "one nature of the incarnate Word", using the Greek word mia (meaning one in the sense of united) rather than monos (meaning one in isolation). Hence, as the Agreement states, the correct term for these Churches is Miaphysite, not Monophysite.

Cyril speaks of a "hypostatic union", meaning a union of divinity and humanity in Christ from the very core of his personal being. Cyril can also be seen as anticipating later kenotic Christologies, in which the radical self-giving of God in the incarnation - his emptying of himself, as Paul puts it in his Letter to the Philippians - comes down in the fullness of divine love to the lowest part of our human need.

In speaking of the nature of Christ and of the cost of our salvation, Christians have needed to say that in Jesus Christ we see one who is fully human, not someone whose humanity is only in appearance; but equally that Jesus Christ is the one in whom "the fullness of the Godhead dwells". Ultimately, how this is so is a mystery that stretches human language, but the reality of this incarnation is at the very heart of our Christian faith.

ANGLICANS have had a long relationship with the Oriental Orthodox churches since the mid-19th century, when Queen Victoria sent a printing press to Patriarch Peter of the Syrian Church. (The Patriarch's portrait hangs in Lambeth Palace.) After an earlier Anglican-Oriental Orthodox forum, the new commission agreed to study Christology. At the very first meeting, in Etchmiadzin, Armenia, in 2002, a draft statement on Christology was agreed. This was subsequently sent for comment to the Oriental Churches and to the Provinces of the Anglican Communion.

When the Dialogue - interrupted because of the controversy over the consecration of Bishop Gene Robinson in the United States - resumed last year, some of the responses received were considered, and full consideration was given to them at the meeting of the commission in Cairo this October. It was with great joy that we were able to agree a significant Christological statement.

This is not an isolated agreement. It builds on similar agreements between the Byzantine Orthodox and the Oriental Orthodox in 1989 and 1990, on the Driebergen agreement between the Reformed Churches and the Oriental Orthodox in 1994, and on the joint statements between Pope John Paul II and visiting heads of the Oriental Orthodox Churches. Thus this new agreement is part of a wide ecumenical endeavour to overcome this most ancient of Christian divisions on a major matter of doctrine. Metropolitan Bishoy, my Oriental Orthodox opposite number, believes the Anglican-Oriental Orthodox Agreement to be the best and most substantial of all these agreements.

Inevitably, the agreement is concerned with the technical Greek terms which were involved in the early divisions. But it recognises the limits of all theological language and the philosophical terminology of which it makes use: "We are unable to net and confine the mystery of God's utter self-giving in the incarnation of the divine Word in an ineffable, inexpressible and mysterious union of divinity and humanity, which we worship and adore."

The agreement cites words of Richard Hooker: "It is not man's ability either to express perfectly or to conceive the manner of how (the incarnation) was brought to pass," and cites Hooker's emphasis on the importance of St Cyril's insistence on the unity of the divinity and humanity in the single person of Christ.

The agreement concludes with the words: 'The Son of God emptied himself and became human, absolutely free from sin, in order to transform our fallen humanity to the image of his holiness. This is the gospel we are called to live and proclaim.'

Given the perilous situation of many of these Churches in the Middle East, faced with Islamist persecution, this unity in faith is something in which we can all rejoice.

The Rt Revd Dr Geoffrey Rowell was formerly the Bishop in Europe.