Because the world attracts us by its beauty, abundance, and variety, it is not easy to turn away from it unless in the beauty of visible things one loves the Creator rather than the creature; for when the Creator says: You shall love the Lord your God with all your heart and with all your mind and with all your strength, he shows that it is not his will for us to loosen the bonds of our love for him in any respect whatever. And by joining to this precept love of our neighbor, he commands us to imitate his own goodness, loving what he loves and doing what he does.
Leo the Great (AD 400-461), Tractate 90, 2-3: CCL 138A, 558-561
Leo is perhaps most famous for writing what became the orthodox formulation of Christ's nature at the Council of Chalcedon in AD 451. Although the Oriental Orthodox churches (notably in Syria, as led principally by the ardent Monophysite, Philoxenus of Mabbug) did not accept Leo's formulation, his epistle to the council was greeted with ecstatic praise: "Peter has spoken through Leo!" Leo described how Christ was one person possessing both a divine and a human nature in perfect unison, thus renouncing the Nestorians. He also emphasized that Christ had a divine and a human will in perfect harmony, thus renouncing the Monothelites ("one-willers"). The technical name for this orthodox teaching is the hypostatic union. A hypostasis is a Greek concept for the individuating principle in an entity. Roughly speaking, a hypostasis is a person. Thus, Christ, as one person, possesed two perfect natures (or, ousia) in a "hypostatic union."
Fortunately, centuries of philosophical anf theological inquiry have brought most people to the conclusion that the Oriental rejection of the Chalcedonian (that is, Eastern and Western) belief in Christ's nature was based more on a technical miscommunication, rather than a fundamental doctrinal disagreement. In other words, both sides were saying the same thing in other words. Considering how central the Incarnation is in Christianity, it's remarkable how the Oriental, Eastern and Western wings of the Church share so many varied beliefs, even despite this ancient difference between the former and the latter two. We can only hope this new insight into what all sides are saying will help foster a union between these ancient, but divided, brethren in the Faith. Let us pray.