There is a persistent criticism of the Catholic Church in recent years by traditionalists of various stripes who cannot fathom ecumenism as anything other than a corruption of the Catholic faith. On their view, doctrinal truth was inherited from the Apostles, it never changes, and is preserved by the Church in exactly the same form it was received. There is no development, no dialogue between believers and non-believers, or schismatics, or heretics, as there exists only the possibility for willful misunderstanding of what are always the same statements. There is no room for innocent misinterpretation, nor for development in the doctrinal statements, nor even (worst of all) for developing doctrinal understanding. They view efforts at pursuing ecumenism, particularly the endorsement of it officially at the Second Vatican Council, as nothing other than an attempt to revive a heresy called "modernism" (the belief that doctrine can, has changed, or must change into something other than the apostolic faith, in keeping with the times) and to believe that Truth with a capital "T" changes over time. As a blog I will keep nameless put it, they see ecumenical statements that Vatican II endorsed as being founded on two principles: "2+2=3" and "all we all really need is love."
Despite the ways in which people misinterpret ecumenism and dialogue, I believe that ecumenism cannot be anything other than a "mark" of the true Church (i.e., one of the signs by which we tell the true Church which Christ founded apart from imitations and heresies). It is one of the chief reasons, in fact, that I am not a traditionalist of the stripe mentioned above.
The opposite problem, which results very often from those who see "dialogue" as a solution to all difficulties, is to fall back on a belief that "only behavior matters." Beliefs, on this view, are dispensable, optional. Orthodoxy is unimportant; only ortho-praxis (right action) is. The Church needs to put aside its medieval beliefs about things like sin, evil, that fornication, contraception, or adultery remain sins, and that Christ instituted a hierarchy that can teach infallibly in His name. All we really need is love. We can forgive living in adultery because there is nothing there to forgive in the first place. The truth is bigger than anything anyone knows and therefore, they claim, we can only guess and doubt, leaving our own beliefs as not literally true, but only as what I grew up believing. Their attitude is: "Who am I to say that Buddhism, or Islam, or any other religion is not a way to heaven? How can I say I have 'The Truth'?"
All of that, of course, is crazy and heretical. Ecumenism needs to be rightly understood. The Church has herself been trying to correct deviant understandings of ecumenism since the Modernist controversies, and we shouldn't delude ourselves into forgetting that those bad views persist among some people today. We can't be naive and foolish in how we do ecumenism, nor does it mean that everybody can "do" ecumenical dialogue in the way a theologian, who knows the ins-and-outs of doctrinal complexity, can do it. Nevertheless, one need not throw out the baby with the bath water. In fact, to do so - to reject ecumenism in principle - is, at least in my view, to become nothing other than a heretic.
I was reading a post at the National Catholic Register by Father Dwight Longenecker that tried to point to the problems in the Church today which result from a breakdown of properly-understood dialogue, and I cannot agree more. In a fitful reaction against a real evil - the bad ecumenical modernist described above - many people ignored the critical truth at the center of ecumenism: that one cannot be orthodox, let alone charitable, without being ecumenical.
Technically defined, "ecumenism" is the attempt to seek corporate ecclesial reconciliation and unity among all the separated Christian bodies, so that they form one Church and one faith. It is my view that ecumenism is only the other side of a love for orthodoxy and a hatred for heresy. Ecumenism is nothing other than a living concern for doctrinal integrity and wholeness. It is a deep and loving desire to bring other people to discover the truth about God and the Church, because, without that, they cannot make it to heaven.
Rather than try to explain why this is so, all one needs to do is causally glance over the history of heresy and the way in which the Church Fathers reacted to it. One of the greatest defenders of doctrinal orthodoxy of all time, Saint Athanasius, a man who went into exile across the entire Mediterranean because he could not renounce belief in the consubstantiality of the Son with the Father, is a perfect example of true ecumenism. On one hand, we know that he fought for the Nicene formula that the Son was "one in substance" and did not see anything in Arianism but a spiritual disease that had to be eradicated from the Body of Christ.1
But, on the other, Athanasius was moved with pity for those led astray by the heretics and sought on every opportunity to recall them to the faith. Even in holding that Arius' doctrine was a poison, the sinner was loved. Excommunication was not to abandon the other person, but to draw them back to Catholic truth and unity. This is the reason Athanasius set about showing the Arians, with rational arguments, where they had gone wrong, devoting tract after tract to the cause. His efforts in seeking the agreement of Rome and the West was a love of unity in the truth - to ensure that everybody was living in peace, a peace in unity of faith. Even when it came to doctrinal formulations, Athanasius was willing to discuss the possibility of terminological differences in the Nicene Creed, negotiating with certain sects of the "semi-Arians" to find room for differences.2 All of this aside from the fact, too, that many of Athanasius' most famous writings - On the Incarnation and Against the Heathen - were written to move non-Christians to conversion.
Ironically, it was Athanasius' calm and reasoned appeal to the semi-Arians in De Synodis that won a young monk to the cause of orthodoxy and made yet another champion of the faith. The young monastic was St. Basil of Caesarea, who, on being ordained a bishop, followed a course of defending the Catholic faith against heretics in much the same manner as Athanasius. On one hand, he saw the importance of the doctrinal concerns and wanted nothing less than complete destruction of heresy. On the other, he worked tirelessly to seek union and charity, admitting senses of doctrinal phrasing which, while not his own, preserved the truth of the faith. The end of his most famous On the Holy Spirit illustrates his feelings:
Now there is no one to receive the weak in faith, but mutual hatred has blazed so high among fellow clansmen that they are more delighted at a neighbour's fall than at their own success. Just as in a plague, men of the most regular lives suffer from the same sickness as the rest, because they catch the disease by communication with the infected, so nowadays by the evil rivalry which possesses our souls we are carried away to an emulation in wickedness, and are all of us each as bad as the others.
For all these reasons I ought to have kept silence, but I was drawn in the other direction by love, which seeks not her own, and desires to overcome every difficulty put in her way by time and circumstance. [...] Wherefore we too are undismayed at the cloud of our enemies, and, resting our hope on the aid of the Spirit, have, with all boldness, proclaimed the truth. Had I not so done, it would truly have been terrible that the blasphemers of the Spirit should so easily be emboldened in their attack upon true religion, and that we, with so mighty an ally and supporter at our side, should shrink from the service of that doctrine, which by the tradition of the Fathers has been preserved by an unbroken sequence of memory to our own day.3
Finally, as the crown on the witness of the Fathers, is Saint Augustine of Hippo. The Donatist schism, which sought to separate the "pure" Christians from the impure, and denied the validity of sacraments performed by Catholic ministers or those in communion with them, led him to devote the last half of his life to untiring attempts not only to counter their views, but to seek true and lasting union. Even without any further background on the controversy, it is a stunningly beautiful testimony to the true spirit of Catholic ecumenism:
We entreat you, brothers, as earnestly as we are able, to have charity, not only for one another, but also for those who are outside the Church. Of these some are still pagans, who have not yet made an act of faith in Christ. Others are separated, insofar as they are joined with us in professing faith in Christ, our head, but are yet divided from the unity of his body. My friends, we must grieve over these as over our brothers. Whether they like it or not, they are our brothers; and they will only cease to be so when they no longer say our Father.
The prophet refers to some men saying: When they say to you: You are not our brothers, you are to tell them: You are our brothers. Consider whom he intended by these words. Were they the pagans? Hardly; for nowhere either in Scripture or in our traditional manner of speaking do we find them called our brothers. Nor could it refer to the Jews, who did not belive in Christ. Read Saint Paul and you will see that when he speaks of "brothers," without any qualification, he refers always to Christians. For example, he says: Why do you judge your brother or why do you despise your brother? And again: You perform iniquity and commit fraud, and this against your brothers.
Those then who tell us: You are not our brothers, are saying that we are pagans. That is why they want to baptize us again, claiming that we do not have what they can give. Hence their error of denying that we are their brothers. Why then did the prophet tell us: Say to them: You are our brothers? It is because we acknowledge in them that which we do not repeat. By not recognizing our baptism, they deny that we are their brothers; on the other hand, when we do not repeat their baptism but acknowledge it to be our own, we are saying to them: You are our brothers.
I they say, "Why do you seek us? What do you want of us?" we should reply: You are our brothers. They may say, "Leave us alone. We have nothing to do with you." But we have everything to do with you, for we are one in our belief in Christ; and so we should be in one body, under one head.
And so, dear brothers, we entreat you on their behalf, in the name of the very source of our love, by whose milk we are nourished, and whose bread is our strength, in the name of Christ our Lord and his gentle love. For it is time now for us to show them great love and abundant compassion by praying to God for them. May he one day give them a clear mind to repent and to realize that they have nothing whatever to say against the truth; they have nothing now but the sickness of their hatred, and the stronger they think they are, the weaker they become. We entreat you then to pray for them, for they are weak, given to the wisdom of the flesh, to fleshly and carnal things, but yet they are our brothers. They celebrate the same sacraments as we, not indeed with us, but still the same. They respond with the same Amen, not with us, but still the same. And so pour out your hearts for them in prayer to God.4
There are of course many other things that could be said, but St. Augustine makes perfectly clear why ecumenism is not optional. It is part and parcel of Christian love to seek to dialogue with separated Christians, to work with them for unity, to seek improved doctrinal understanding and spiritual conversion of heart. If one really loves the Church and unity in her, believing one cannot be saved except in the Church, one has a duty not to drive people away and instead to seek out the lost and the fallen. It is nothing other than to live out in our own lives the ministry of the Good Shepherd. If one loves doctrinal truth and hates heresy, one will fight error, instruct those who were taught poorly, and look for every opportunity to reconcile doctrinal differences.
The final note to this story is that this - the fact that Catholics seek unity in a spirit of love and faith - is a "mark" of the true Church. We can tell which is the Church of Jesus Christ because it remains the Church today that values visible unity, that wants all men to be saved and come to the knowledge of the truth, and that continues to reach out to those separated from her. It was not the Donatists who sought out unity. It was not the Arians, who only sought unity by force, attempting to get the government to punish those who did not agree with them. Rather, the Catholic Church sought mutual understanding and unity, working out painstakingly difficult doctrinal formulations in synods or ecumenical councils.
In our own recent age, the Second Vatican Council was the most visible sign of this. It reached out to reunify with the Orthodox Churches, to open better channels of dialogue with Protestant churches, and even to offer kind words of reconciliation to Jews, Muslims, and atheists. None of these attempts denied the Catholic faith, none compromised the precious treasure of the apostolic doctrinal heritage, but that did not stop the Church from reaching out time and time again to those outside of her communion.5 Dialogue and the duties of love were never optional.
We too can pick up the call to understanding, dialogue, and prayer. Consider praying a daily Rosary or a decade of the Rosary for the reunion of all. Maybe you have a family member or friend who you want to pray for in particular. Think about inviting a non-Catholic friend to come to church on Sunday or to a Vespers service. Perhaps, in our own day, the examples of Athanasius, Basil, and Augustine can serve to show us how to better love our own faith, to defend it, and to love those who do not profess it - God-willing - yet.