One often hears in ecumenical circles that "the walls that separate the churches do not reach the heavens". These words are justly disputed by Archbishop Seraphim (Sobolev) who says that "these separating walls, i.e. divisions between the Orthodox Church and the heretics, began taking place at the Ecumenical Councils. The purpose of these divisions was the preservation of the Orthodox faith from being destroyed through merging with perilous heresies. These divisions took place in fulfillment of Christ's words:
"Suppose ye that I am come to give peace on earth? I tell you, Nay; but rather division" (Luke 12, 51). Ecumenical Councils, too, fulfilled the words of our Lord addressed to His Apostles and their successors -- bishops who govern the Orthodox Church:
"Verily I say unto you, whatsoever ye shall bind on earth shall be bound in heaven: and whatsoever ye shall loose on earth shall be loosed in heaven" (Mt. 18, 18). It is clear that these divisions do reach heaven. How would it be possible for these divisions to stop short of reaching Christ, when they are based on the words uttered by Christ the Savior Himself?!" 
One should always remember that dogmatic resolutions of Ecumenical Councils containing anathema against heretics were carried out in agreement with the words of the Apostles:
"For it seemed good to the Holy Ghost, and to us" (Acts 15, 28). This means that the resolutions against heretics originated not only from the Church Fathers but also from the
Holy Spirit Himself . The Holy Tradition of the Orthodox Church and the definitions reached by the Ecumenical and Local Councils "followed the royal path in agreement with the Divine teaching of our Holy Fathers and the Tradition of the Church, being aware that they were of the Holy Spirit abiding in the Church" .
In their utter impudence, ecumenists openly accuse the Orthodox Church of the sin of division. It is true that they do not attribute this sin exclusively to the Orthodox Church, but also to all "Christians".
But the Orthodox Church is not to blame for the falling away of heretics. Confession of faith and martyrdom were taken up by true believers who wished to remain faithful to Christ and His Church. If it were not for this holy effort, the truth of Orthodoxy would have blended with heretical lies, and this would have meant the disappearance of the Orthodox Church itself. But
"the gates of hell shall not prevail against it (the Church)" (Mt. 16, 18) despite the extreme ferocity of its enemies in our times. Orthodox Christians must oppose the pernicious lies of contemporary heresy of ecumenism with the truth of our Holy Tradition. Because the Orthodox Church has preserved the continuous and immutable Holy Tradition, it has at all times and everywhere preserved the same pure confession of faith, the same religious observances, the same basic laws of its organization, the same hierarchical structure which it received at the very beginning of its existence on earth. All this, then, constitutes the ever undivided spirit of Orthodoxy, its wholeness and sanctity.
As to the perceived indifference to the non-Orthodox of which ecumenists like to reproach Orthodox Christians, anyone even slightly familiar with Orthodoxy knows that we pray for those in error. Every member of the Church knows that we raise our prayer to the Lord
"that with the light of His divine Reason He may enlighten the minds of those who have been blinded by unbelief, and that by the power of the Holy Spirit He may convert all who have erred to knowledge of the truth and join them to His chosen flock" (from the Rite of Orthodoxy) .
The Holy Orthodox Church has always prayed for and will continue praying for the return of those gone astray:
"O Lord, with the light of the knowledge of Thee illumine those who have fallen away from the Orthodox Faith, and join them to Thy holy, apostolic and universal Church" (from the Commemoration appended to the Psalter) .
Great indeed, would be the joy for repentant sinners (Luke 15, 10), if those who have fallen away from the Orthodox Church were to hear our prayers and return to the only Church of salvation. But as long as they persist in their error, and keep looking for doctrinal, sacramental and moral compromises unacceptable to Orthodox Christians; as long as they set themselves against the Church and its divinely revealed and patristic truths, it is impossible for us to communicate with them in prayer, remembering the words of Apostle Paul:
"A man that is an heretic after the first and second admonition, reject" (Tit. 3,10)
On the contrary, while violating canons and praying with heretics, ecumenists inculcate and foster confessional indifference, renovations and heretical teachings frankly hostile to Orthodoxy in Orthodox Christians.
It is well known that ecumenism lowers the requirements indispensable for the unification of Christians by reducing them solely to an acknowledgment of Jesus Christ as God. Yet many Protestant sects and groups, not to speak of other heretics, do not even recognize the Divinity of our Savior! This denigration of the Christian doctrine to such a humiliating minimum of faith is unacceptable for the Orthodox, because such "faith" is below that of the devils (James 3, 19; Mt. 8, 8, 29; Mark 5, 7)
Perhaps most frequently, the ecumenists like to quote the words of Christ's High-priestly prayer:
"that they all may be one; as Thou, Father, art in Me, and I in Thee, that they also may be one in Us; that the world may believe that Thou has sent Me. And the glory which Thou gavest Me I have given them; that they may be one, even as We are one" (John 17, 21-22)
It is very significant that when quoting the Saviors words:
"that they all may be one", ecumenists invariably omit the preceding words of the Prayer which make it clear that the Savior does not mean all the people in the world, but only all the
true believers in Him: "I pray for them:
I pray not for the world, but for them which Thou hast given Me...
that they may be one, as We are" (John 17, 9-11).
"Neither pray I for these alone, but for them also which shall believe on Me through their word;
that they all may be one" (John 17, 20-21). These words of Christ make it obvious that only those who have the
true faith in Him may form true unity. These words do not speak of a perfunctory union of all the false teachings and heresies, but of being joined in truth.
Ecumenists maintain that any
path may lead to salvation. Speaking of Christ they define Him only as the
way, avoiding the Gospel definition of the Lord as the
truth and the life (John 14,6).
The danger of ecumenism lies in the fact that it conceals its cunning under the guise of all-reconciling "charity". However, the "love" preached by ecumenism is deprived of truth. St. Paul says that
"love (charity) rejoiceth in the truth" (1 Cor 13,6).
He calls on us to speak "the truth in love" (Ephes. 4,15) 
The Holy Scripture calls God the absolute
Truth (Jer. 10,10; John 14,6) and the absolute
Love (1 John 4,8). This means that Truth and Love are essentially
one. As truth and love are bound in God, so they must be bound in people. Whoever wishes to be saved, must follow not only the path of love, but also the path of truth. On the other hand, a display of "love and condescension" to those gone astray is a
betrayal of truth, and therefore, a
betrayal of love. 
 Archbishop Seraphim (Sobolev), lecture "Should the Russian Orthodox Church take Part in the Ecumenical Movement?" in the Collection "The Acts of the Conference of the Heads and the Representatives of the Autocephalous Orthodox Churches...", vol. 2, Moscow, 1949, p. 373.
 Ibid., p. 374.
 The collection of the Mt. Athos Russian St. Elias Skete "Uchenie Pravoslavnoi Tserkvi o Sviashchennom Predanii i otnoshenie eia k novomu stiliu" (The teaching of the Orthodox Church on the Holy Tradition and its Attitude to the New Style), Published by the Holy Trinity Monastery, Jordanville, N.Y., USA, 1989, p. 16.
 "Posledovanie molebnago peniia "O obrashchenii zabludshikh" pevaemago v nedeliu Pravoslaviia i vo inykh potrebnykh sluchaiakh" (The rite of the prayer service "On the Conversion of Those Gone Astray" which is sung during the Week of Orthodoxy or on the other needful occasions), St.Petersburg., 1902, p-8, 16.
 From the text of the "Pomiannik" (The Book of Commemoration) -- the supplement to the Psalter.
 See Archimandrite Seraphim (Aleksiev), Archimandrite Sergii (Yazadzhiev), "Why an Orthodox Christian Must Not be an Ecumenist", p. 243.