Question:
Answer:
But even if we or an angel from heaven should preach [to you] a gospel other than the one that we preached to you, let that one be accursed! As we have said before, and now I say again, if anyone preaches to you a gospel other than the one that you received, let that one be accursed! (Gal. 1:8-9)
But I am afraid that, as the serpent deceived Eve by his cunning, your thoughts may be corrupted from a sincere [and pure] commitment to Christ. For if someone comes and preaches another Jesus than the one we preached, or if you receive a different spirit from the one you received or a different gospel from the one you accepted, you put up with it well enough. . . For such people are false apostles, deceitful workers, who masquerade as apostles of Christ. (2 Cor. 11:3-4, 13)
In the early Church the Apostles were the guarantee of the truth of what was said. If it was in accordance with what the Apostles preached it could be considered true, if it was in contradiction it could be considered false. Today we have the Church as the successor to the Apostles, and if someone preaches in opposition to the Church it is to be considered false (Luke 10:16).
Sometimes it is easy because the preacher rejects the Trinity, the divinity of Jesus or another essential element of our faith. Other times it is less obvious and we need to be sure to give our careful attention to how the Church judges the matter.