Then He strictly warned them that they should tell no one about Him. And He began to teach them that the Son of Man must suffer many things, and be rejected by the elders and chief priests and scribes, and be killed, and after three days rise again. He spoke this word openly. Then Peter took Him aside and began to rebuke Him. But when He had turned around and looked at His disciples, He rebuked Peter, saying, “Get behind Me, Satan! For you are not mindful of the things of God, but the things of men.” When He had called the people to Himself, with His disciples also, He said to them, “Whoever desires to come after Me, let him deny himself, and take up his cross, and follow Me.
Beware of the wicked
St. Ignatius of Antioch, Epistle to the Philadelphians, Chapter III, 1-3, Chapter IV, 1, in Fathers and Church Writers (1979), vol. 1, p. 179
“Beware of the evil weeds which Christ does not cultivate, for they are not planted by the Father (Matthew 15:13). I do not speak this because I have found division among you, but rather purity. For all who belong to God and Jesus Christ are with the bishop. And all who repent and come to the unity of the Church will also belong to God, so that they may live according to Jesus Christ. Do not deceive yourselves, my brothers, if anyone follows those who cause division, they will not inherit the Kingdom of God (1 Corinthians 6:9-10). If anyone follows foreign teachings, they are not in harmony with the passions of Christ.
Therefore, strive to participate in one Eucharist, for there is one Body of our Lord Jesus Christ and one Chalice for the unity with His Blood. There is one altar, just as there is one bishop along with the priests and deacons, who are together with me as servants. So whatever you do, do it according to God.”
St. Ignatius of Antioch, Epistle to the Smyrnaeans, Chapter IV, 1, in Fathers and Church Writers (1979), vol. 1, p. 183.
“I give you these pieces of advice, my beloved; even though I know that you think the same way as I do. But I want to protect you from those who are like savage beasts in human form, whom you must not only refuse to welcome but, if possible, not even meet with. Instead, pray for them, perhaps they may repent, although it is a difficult thing.”
St. Ignatius of Antioch, Epistle to the Smyrnaeans, Chapter VII, in Fathers and Church Writers (1979), vol. 1, p. 184.
“It is fitting, therefore, to stay away from such people and not speak with them, either privately or publicly. Let us hold fast to the prophets and, above all, to the Gospel, in which the sufferings are revealed to us and the resurrection is accomplished. Flee from divisions, for they are the beginning of evils.”