The True Faith Overthrows Heresy
Therefore, heresy is so-called from the Greek word meaning choice, by which each chooses according to his own will what he pleases to teach or believe. But we are not permitted to believe whatever we choose, nor to choose whatever someone else has believed. We have the Apostles of God as authorities, who did not themselves of their own will choose what they would believe, but faithfully transmitted to the nations the teaching received from Jesus Christ. So, even if an angel from heaven should preach otherwise, he shall be called anathema. – Bishop Saint Isidore of Seville, Spain
The letter below was written by St. Athanasius of Alexandria (296 AD – d. 2 May 373) to the early Christians of the 4th century who refused to accept the Arian heresy, Christians who had lost their Church buildings to the heretics, but Christians who kept the faith.
“May God console you! … What saddens you … is the fact that others have occupied the churches by violence, while during this time you are on the outside. It is a fact that they have the premises — but you have the apostolic faith. They can occupy our churches, but they are outside the true faith. You remain outside the places of worship, but the faith dwells within you. Let us consider: what is more important, the place or the faith? The true faith, obviously. Who has lost and who has won in this struggle — the one who keeps the premises or the one who keeps the faith?
True, the premises are good when the apostolic faith is preached there; they are holy if everything takes place there in a holy way …
You are the ones who are happy; you who remain within the Church by your faith, who hold firmly to the foundations of the faith which has come down to you from apostolic tradition, and if an execrable jealously has tried to shake it in a number of occasions, it has not succeeded. They are the ones who have broken away from it in the present crisis.
No one, ever, will prevail against your faith, beloved brothers, and we believe that God will give us our churches back some day.
Thus, the more violently they try to occupy the places of worship, the more they separate themselves from the Church. They claim that they represent the Church but in reality they are the ones who are expelling themselves from it and going astray.
Even if Catholics faithful to tradition are reduced to a handful, they are the ones who are the true Church of Jesus Christ.”
(Coll. Selecta SS. Eccl. Patrum. Caillu and Guillou, Vol. 32, pp 411-412)