Justinian has clearly stated that basic principle of the Byzantine political system in the preface to his Sixth Novel, dated March 16, 535:
There are two major gifts which God has given unto men of His supernal clemency, the priesthood and the imperial authority – hierosyne and basileia; sacerdotium and imperium. Of these, the former is concerned with things divine; the latter presides over the human affairs and takes care of them. Proceeding from the same source, both adorn human life. Nothing is of greater concern for the emperors as the dignity of the priesthood, so that priests may in their turn pray to God for them. Now, if one is in every respect blameless and filled with confidence toward God, and the other does rightly and properly maintain in order the commonwealth entrusted to it, there will be a certain fair harmony established, which will furnish whatsoever may be needful for mankind. We therefore are highly concerned for the true doctrines inspired by God and for the dignity of priests. We are convinced that, if they maintain their dignity, great benefits will be bestowed by God on us, and we shall firmly hold whatever we now possess, and in addition shall acquire those things which we have not yet secured. A happy ending always crowns those things which were undertaken in a proper manner, acceptable to God. This is the case, when sacred canons are carefully observed, which the glorious Apostles, the venerable eye-witnesses and ministers of the Divine World, have handed down to us, and the holy Fathers have kept and explained.
Justinian did not speak of State, or of Church. He spoke of two ministries, or of two agencies, which were established in the Christian Commonwealth. They were appointed by the same Divine authority and for the same ultimate purpose. As a “Divine gift,” the Imperial power, imperium, was “independent” from the Priesthood, sacerdotium. Yet it was “dependent” upon, and “subordinate” to, that purpose for which it had been Divinely established. This purpose was the faithful maintenance and promotion of the Christian truth. Thus, if “the Empire” as such was not subordinate to the Hierarchy, it was nevertheless subordinate to the Church, which was a Divinely appointed custodian of the Christian truth. In other words, the Imperial power was “legitimate” only within the Church. In any case, it was essentially subordinate to the Christian Faith, was bound by the precepts of the Apostles and Fathers, and in this respect “limited” by them. The legal status of the Emperor in the Commonwealth depended upon his good standing in the Church, under her doctrinal and canonical discipline. Imperium was at once an authority, and a service. And the terms of this service were set in rules and regulations of the Church. In his coronation oath, the Emperor had to profess the Orthodox faith and to take a vow of obedience to the decrees of the ecclesiastical Councils. This was no mere formality. “Orthodoxy was, as it were, the super-nationality of Byzantium, the basic element of the life of the State and people” (I. I. Sokolov).
Fr. Georges Florovsky