What does the Bible say about being deceived in the faith?

The Apostle John, in 2 John 7-9, cautions believers about the presence of deceivers in the world who do not acknowledge that Jesus Christ has come in the flesh, labeling them as deceivers and antichrists. He emphasizes the necessity of adhering to the doctrine of Christ, declaring that those who do not abide in this doctrine do not have God. This highlights the critical importance of sound doctrine in the Christian faith, as it is through the true teaching of Christ that one can claim both the Father and the Son.