"[The Byzantine Empire's constitution] was based on a clear religious conviction: that it was the earthly copy of the Kingdom of Heaven. (…)
"It saw itself as the universal Empire. Ideally it should embrace all the peoples of the earth, who, ideally, should all be members of the one true Christian Church, its own Orthodox Church.
"Just as man was made in God’s image, so man’s kingdom on earth was made in the image of the Kingdom of Heaven. Just as God ruled in Heaven, so an Emperor, made in his image, should rule on earth and carry out his commandments.
"Evil had made its way into God’s creation, and man was stained with sin. But if the copy – the Greek word was mimesis, ‘imitation’ – could be achieved, with the Emperor and his ministers and counselors imitating God with His archangels and angels and saints, then life on earth could become a proper preparation for the truer reality of life in Heaven. (…)
"Constantine was lucky in having as his biographer and panegyrist Eusebius of Caeserea (….).
"According to Eusebius the triumph of history had now come, when the Roman Emperor had accepted the Christian message. He was now the wise king who was the imitation of God, ruling a realm which could now become the imitation of Heaven. (…)
"The king is not God among men but the Viceroy of God. He is not the logos incarnate but is in a special relation with the logos. He has been specially appointed and is continually inspired by God, the friend of God, the interpreter of the Word of God. His eyes look upward, to receive the messages of God. He must be surrounded with the reverence and glory that befits God’s earthly copy; and he will ‘frame his earthly government according to the pattern of the divine original, finding strength in its conformity with the monarchy of God’.
"…by and large, the Eusebian constitution survived in Byzantium down the centuries. It was never a legal constitution, so it could be adapted to suit the needs of the time. Roman traditions lasted on to temper it and remind the Emperor that while he represented God before the people, it was his duty also to represent the people before God.
"It never took root in the West, where it faded out when the practical power of the Empire declined. Western thought preferred the rival conception of Saint Augustine’s City of God.
"But to Byzantium it gave a sense of unity, of self-respect and of divine purpose that sustained the Empire to the last. (…)
"No form of government can survive for very long without the general approval of the public. (…) The ordinary man and woman in Byzantium believed their Empire to be God’s holy empire on earth, with the holy Emperor as representative of God before the people and the representative of the people before God.
"For eleven centuries (…) the theocratic constitution of the Christian Roman Empire was essentially unchanged.
"No other constitution in all the history of the Christian era has endured for so long."
From: Steven Runciman. The Byzantine Theocracy. Cambridge University Press, 1977.
The Byzantine Empire was the most sustainedly-devout Christian society of history so far, and it also had the most enduring political constitution.
This combination gives Byzantium an unique status.
Byzantium is therefore deserving of particular study and reflection; and, for Christians, the essence of Byzantium might legitimately serve as an ideal aim for worldly human society.