How important is sound, orthodox Christian faith? Read an early church father, Irenaeus, on the matter:
"There are also those who heard from [Polycarp] that John, the disciple of the Lord, going to bathe at Ephesus, and perceiving Cerinthus within, rushed out of the bath-house without bathing, exclaiming, 'Let us fly, lest even the bath-house fall down, because Cerinthus, the enemy of the truth, is within.'"
Despite the gravity of the situation, I find it funny that the Apostle John would yell, "Hey, let's get out of here before this place caves in!"
"And Polycarp himself replied to Marcion, who met him on one occasion, and said, 'Do you know me?' 'I do know you, the first-born of Satan.'"
Marcion is my favorite historical heretic; I mean, that guy really knew how to be a false prophet! With Polycarp's zinger I have to judge that he had one of the best one-liners in eccleciastical history!
Irenaeus then comments:
"Such was the horror which the apostles and their disciples had against holding even verbal communication with any corrupters of the truth; as Paul also says, 'A man that is a heretic, after the first and second admonition, reject; knowing that he that is such is subverted, and sins, being condemned of himself.'" (Tit 3:10) (Against Heresies, Book 3, Chapter 3.4)
May the gospel be so clear to us that we know from whom to run!