Paul faced much opposition, not just from those outside the church, but from genuine Christians and from imposters who were mistakenly accepted by some in the church as Christians. Some of the most uncomfortable parts of Paul’s letters are where he feels pressured into defending his spiritual authority (and hence the accuracy of his teachings) to Christians were beginning to be persuaded by people in the church who were teaching other doctrines. Here are some Scriptures that hint at this:

1 Corinthians 4:15 For though you have ten thousand tutors in Christ, yet not many fathers. For in Christ Jesus, I became your father through the Good News.

1 Corinthians 9:2 If to others I am not an apostle, yet at least I am to you . . .

2 Corinthians 11:20  . . . you even put up with anyone who enslaves you or exploits you or takes advantage of you or pushes himself forward . . . (NIV)

2 Corinthians 3:1-2 Are we beginning again to commend ourselves? Or do we need, as do some, letters of commendation to you or from you? You are our letter, written in our hearts, known and read by all men

Galatians 2:11-13 But when Peter came to Antioch, I resisted him to his face, because he stood condemned. . . . the rest of the Jews joined him in his hypocrisy; so that even Barnabas was carried away with their hypocrisy.

Galatians 3:1 Foolish Galatians, who has bewitched you not to obey the truth . . .

Galatians 4:19 My little children, of whom I am again in travail until Christ is formed in you

Acts 15:24  . . . we have heard that some who went out from us have troubled you with words, unsettling your souls . . .

Philippians 1:15-17 Some indeed preach Christ even out of envy and strife, and some also out of good will. The former insincerely preach Christ from selfish ambition, thinking that they add affliction to my chains . . .

2 Timothy 2:25 in gentleness correcting those who oppose him: perhaps God may give them repentance leading to a full knowledge of the truth

2 Timothy 4:16 At my first defense, no one came to help me, but all left me. May it not be held against them.

Galatians 2:4 This was because of the false brothers secretly brought in, who stole in to spy out our liberty which we have in Christ Jesus, that they might bring us into bondage

2 Corinthians 11:12-13 And I will keep on doing what I am doing in order to cut the ground from under those who want an opportunity to be considered equal with us in the things they boast about. For such men are false apostles, deceitful workmen, masquerading as apostles of Christ. (NIV)

1 Timothy 1:19-20 holding faith and a good conscience; which some having thrust away made a shipwreck concerning the faith; of whom is Hymenaeus and Alexander; whom I delivered to Satan, that they might be taught not to blaspheme.

2 Timothy 2:17-18 those words will consume like gangrene, of whom is Hymenaeus and Philetus; men who have erred concerning the truth, saying that the resurrection is already past, and overthrowing the faith of some.

1 Corinthians 5:4-5 In the name of our Lord Jesus Christ, you being gathered together, and my spirit, with the power of our Lord Jesus Christ, are to deliver such a one to Satan for the destruction of the flesh, that the spirit may be saved in the day of the Lord Jesus.

2 Thessalonians 3:11-12, 14-15 For we hear of some who walk among you in rebellion, who don’t work at all, but are busybodies. Now those who are that way, we command and exhort in the Lord Jesus Christ, that with quietness they work, and eat their own bread. . . . If any man doesn’t obey our word in this letter, note that man, that you have no company with him, to the end that he may be ashamed. Don’t count him as an enemy, but admonish him as a brother.

Romans 16:17 Now I beg you, brothers, look out for those who are causing the divisions and occasions of stumbling, contrary to the doctrine which you learned, and turn away from them.

1 Corinthians 5:11-13  . . . I wrote to you not to associate with anyone who is called a brother who is a sexual sinner, or covetous, or an idolater, or a slanderer, or a drunkard, or an extortionist. Don’t even eat with such a person. For what have I to do with also judging those who are outside? Don’t you judge those who are within? But those who are outside, God judges. “Put away the wicked man from among yourselves.”

Titus 3:10 Warn a divisive person once, and then warn him a second time. . . . (NIV)

1 Corinthians 15:2 by which also you are saved, if you hold firmly the word which I preached to you – unless you believed in vain.