Ecumenism is the common name for the pseudo-Christianity of the pseudo-Churches of Western Europe. Within it is the heart of European humanism, with Papism as its head. All of pseudo-Christianity, all of those pseudo-Churches, are nothing more than one heresy after another. Their common evangelical name is: Pan-heresy. Why? This is because through the course of history various heresies denied or deformed certain aspects of the God-man and Lord Jesus Christ; these European heresies remove Him altogether and put European man in His place. In this there is no essential difference between Papism, Protestantism, Ecumenism, and other heresies, whose name is “Legion.”
Orthodox dogma, that is to say the overriding dogma of the Church, is rejected by them and replaced by the Latin heretical overriding dogma of the primacy and infallibility of the Pope, that is to say of man. From this pan-heresy heresies were born and continue to be born: the Filioque, the rejection of the invocation of the Holy Spirit, unleavened bread, the introduction of created grace, cleansing fire, superfluous works of the saints, mechanized teachings about salvation, and from this sprang mechanized teachings about life, Papocaesarism, the Inquisition, indulgences, the murder of sinners because of their sins, Jesuitism, the scholastics, the casuists, Monarchianism, and social individualism of different kinds…
From the chapter “Humanistic Ecumenism” in Orthodox Faith and Life in Christ, by Father Justin Popovich, trans. by Asterios Gerostergios (Belmont, MA: Institute for Byzantine and Modern Greek Studies, 1994), p. 169.