Galatians 1:8-9
However, if we [apostles] or even an angel [claiming to be] from heaven were to preach any other "gospel" than the one we have [already] preached to you, let that person be cut off from God's [salvation].
1 Timothy 4:1-3
Now the Holy Spirit specifically says that in later times [Note: "Later times" in the New Testament usually refers to the period following the first coming of Christ and the establishment of the church], some people will fall away from the faith [i.e., the true teaching of Christianity]. They will pay attention to deceitful spirits [i.e., lying people] and the teaching of evil spirits.
Titus 1:9-10
[He must] hold on firmly to the trustworthy message, which is according to [our] teaching, so that he will be able both to exhort people with sound teaching and to convince those who contradict it.
James 4:8
Come close to God and He will come close to you. Wash your hands, you sinful people [i.e., this is an exhortation to repent of moral and spiritual corruption], and purify your hearts, you double-minded people.
2 Peter 2:1-3
But just as there were false prophets among the people before, there will also be false teachers among you [Christians]. They will privately teach harmful doctrines that destroy people [spiritually], by even denying [that Jesus is] the Master, [and thereby] destroying themselves quickly.
Jude 1:4
For certain men have secretly infiltrated [your ranks]; they are men who had been written about long ago that they should be judged [and condemned] for perverting the unearned favor of our God into [a license for] living unrestrained, indecent lives, and who deny [the identity and work of] our only Master and Lord, Jesus Christ.
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