Ecumenism

St. Ignatius of Antioch: Keep yourselves from those evil plants which Jesus Christ does not tend, because they are not the planting of the Father. Not that I have found any division among you, but exceeding purity. For as many as are of God and of Jesus Christ are also with the bishop. And as many as shall, in the exercise of repentance, return into the unity of the Church, these, too, shall belong to God, that they may live according to Jesus Christ. Do not err, my brethren. If any man follows him that makes a schism in the Church, he shall not inherit the kingdom of God. If any one walks according to a strange opinion, he agrees not with the passion [of Christ.] … Brethren, be not deceived. If any man follows him that separates from the truth, he shall not inherit the kingdom of God; and if any man does not stand aloof from the preacher of falsehood, he shall be condemned to hell. For it is obligatory neither to separate from the godly, nor to associate with the ungodly. If any one walks according to a strange opinion, he is not of Christ, nor a partaker of His passion; but is a fox, a destroyer of the vineyard of Christ. Have no fellowship with such a man, lest ye perish along with him, even should he be thy father, thy son, thy brother, or a member of thy family. For says [the Scripture], “Thine eye shall not spare him.”You ought therefore to “hate those that hate God, and to waste away [with grief] on account of His enemies.”I do not mean that you should beat them or persecute them, as do the Gentiles “that know not the Lord and God;” but that you should regard them as your enemies, and separate yourselves from them, while yet you admonish them, and exhort them to repentance, if it may be they will hear, if it may be they will submit themselves— Epistle to the Philadelphians, Chapter III.

“There is one God, the Father of the living Word, who is His subsistent Wisdom and Power and Eternal Image: perfect Begetter of the perfect Begotten, Father of the only-begotten Son. There is one Lord, Only of the Only, God of God, Image and Likeness of Deity, Efficient Word, Wisdom comprehensive of the constitution of all things, and Power formative of the whole creation, true Son of true Father, Invisible of Invisible, and Incorruptible of Incorruptible, and Immortal of Immortal and Eternal of Eternal. And there is One Holy Spirit, having His subsistence from God, and being made manifest by the Son, to wit to men: Image of the Son, Perfect Image of the Perfect; Life, the Cause of the living; Holy Fount; Sanctity, the Supplier, or Leader, of Sanctification; in whom is manifested God the Father, who is above all and in all, and God the Son, who is through all. There is a perfect Trinity, in glory and eternity and sovereignty, neither divided nor estranged. Wherefore there is nothing either created or in servitude in the Trinity; nor anything superinduced, as if at some former period it was non-existent, and at some later period it was introduced. And thus neither was the Son ever wanting to the Father, nor the Spirit to the Son; but without variation and without change, the same Trinity abides ever.” - A Declaration of Faith, St. Gregory Thaumaturgus

“Having therefore received a charge, and having been fully assured through the resurrection of our Lord Jesus Christ and confirmed in the word of God with full assurance of the Holy Ghost, they (the apostles) went forth with the glad tidings that the kingdom of God should come. So preaching everywhere in country and town, they appointed their first-fruits, when they had proved them by the Spirit, to be bishops and deacons unto them that should believe. And this they did in no new fashion; for indeed it had been written concerning bishops and deacons from very ancient times; for thus said the scripture in a certain place, I will appoint their bishops in righteousness and their deacons in faith.”
- St. Clement of Rome (A.D. 96).

“A brother came to see Abba Macarius the Egyptian, and said to him, ‘Abba, give me a word, that I may be saved.’ So the old man said, ‘Go to the cemetery and abuse [insult] the dead.’ The brother went there, abused [insulted] them and threw stones at them; then he returned and told the old man about it. The latter said to him, ‘Didn’t they say anything to you?’ He replied, ‘No.’ The old man said, ‘Go back tomorrow and praise them.’ So the brother went away and praised them, calling them ‘Apostles, saints and righteous men.’ He returned to the old man and said to him, ‘I have complimented them.’ And the old man said to him, ‘Did they not answer you?’ The brother said no. The old man said to him, ‘You know how you insulted them and they did not reply, and how you praised them and they did not speak; so you too if you wish to be saved must do the same and become a dead man. Like the dead, take no account of either the scorn of men or their praises, and you can be saved.’”