Big-time food for thought:
"Certainly, no one who claims allegiance to Catholic theology can simply declare the doctrine of primacy null and void, especially not if he seeks to understand the objections and evaluates with an open mind the relative weight of what can be determined historically. Nor is it possible, on the other hand, for him to regard as the only possible form and, consequently, as binding on all Christians the form this primacy has taken in the nineteenth and twentieth centuries. The symbolic gestures of Pope Paul VI and, in particular, his kneeling before the representative of the Ecumenical Patriarch were an attempt to express precisely this and, by such signs, to point the way out of the historical impasse. Although it is not given us to halt the flight of history, to change the course of centuries, we may say, nevertheless, that what was possible for a thousand years is not impossible for Christians today. After all, Cardinal Humbert of Silva Candida, in the same bull in which he excommunicated the Patriarch Michael Cerularius and thus inaugurated the schism between East and West, designated the Emperor and people of Constantinople as “very Christian and orthodox”, although their concept of the Roman primacy was certainly far less different from that of Cerularius than from that, let us say, of the First Vatican Council. In other words, Rome must not require more from the East with respect to the doctrine of primacy than had been formulated and was lived in the first millennium. When the Patriarch Athenagoras, on July 25, 1967, on the occasion of the Pope’s visit to Phanar, designated him as the successor of St. Peter, as the most esteemed among us, as one also presides in charity, this great Church leader was expressing the essential content of the doctrine of primacy as it was known in the first millennium. Rome need not ask for more. Reunion could take place in this context if, on the one hand, the East would cease to oppose as heretical the developments that took place in the West in the second millennium and would accept the Catholic Church as legitimate and orthodox in the form she had acquired in the course of that development, while, on the other hand, the West would recognize the Church of the East as orthodox and legitimate in the form she has always had.
"Such a mutual act of acceptance and recognition, in the Catholicity that is common to and still possessed by each side, is assuredly no light matter. It is an act of self-conquest, of self-denunciation and, certainly, also of self-discovery. It is an act that cannot be brought about by diplomacy but must be a spiritual undertaking of the whole Church in both East and West. If what is theologically possible is also to be actually possible in the Church, the theological aspect must be spiritually prepared and spiritually accepted. My diagnosis of the relationship between East and West in the Church is as follows: from a theological perspective, the union of the Churches of East and West is fundamentally possible, but the spiritual preparation is not yet sufficiently far advanced and, therefore, not yet ready in practice. When I say it is fundamentally possible from a theological perspective, I do not overlook the fact that, on closer inspection, a number of obstacles still exist with respect to the theological possibility: from the Filioque to the question of the indissolubility of marriage. Despite these difficulties, some of which are present more strongly in the West, some in the East, we must learn that unity, for its part, is a Christian truth, an essentially Christian concept, of so high a rank that it can be sacrificed only to safeguard what is most fundamental, not where the way to it is obstructed by formulations and practices that, however important they may be, do not destroy community in the faith of the Fathers and in the basic form of the Church as they saw her."
Joseph Cardinal Ratzinger, Principles of Catholic Theology: Building Stones for a Fundamental Theology (San Francisco, CA: Ignatius Press, 1987), pp. 198-199.