Galatians 1:6-9 (NIV) 6 I am astonished that you are so quickly deserting the one who called you by the grace of Christ and are turning to a different gospel-- 7 which is really no gospel at all. Evidently some people are throwing you into confusion and are trying to pervert the gospel of Christ. 8 But even if we or an angel from heaven should preach a gospel other than the one we preached to you, let him be eternally condemned! 9 As we have already said, so now I say again: If anybody is preaching to you a gospel other than what you accepted, let him be eternally condemned!
1 Timothy 1:18-20 (NIV)
18 Timothy, my son, I give you this instruction in keeping with the prophecies once made about you, so that by following them you may fight the good fight, 19 holding on to faith and a good conscience. Some have rejected these and so have shipwrecked their faith. 20 Among them are Hymenaeus and Alexander, whom I have handed over to Satan to be taught not to blaspheme.
Hebrews 6:4-6 (NIV)
4 It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, 5 who have tasted the goodness of the word of God and the powers of the coming age, 6 if they fall away, to be brought back to repentance, because to their loss they are crucifying the Son of God all over again and subjecting him to public disgrace.
