There is no Bible verse that says Paul was either directly or indirectly accused of being a liar. However, given the remarkable circumstances under which he suddenly stopped persecuting the Christians and became an apostle and the foremost witness of Christ to the Gentile nations, 2 Corinthians 11:23-27 goes some way to explaining why Paul was at such pains to convince others he was not a liar:
”Are they servants of Christ? I am a better one—I am talking like a madman—with far greater labours, far more imprisonments, with countless beatings, and often near death. Five times I received at the hands of the Jews the forty lashes less one. Three times I was beaten with rods. Once I was stoned. Three times I was shipwrecked; a night and a day I was adrift at sea; on frequent journeys, in danger from rivers, danger from robbers, danger from my own people, danger from Gentiles, danger in the city, danger in the wilderness, danger at sea, danger from false brothers; in toil and hardship, through many a sleepless night, in hunger and thirst, often without food, in cold and exposure.”
The fact that Paul was seen as strange and questionable, not merely by fellow Jews but also by a number of fellow Jewish Christians, was no doubt hurtful to him. It would be one thing for Paul’s authority and authenticity to be challenged outside the Body of Christ, but inside was a different foe with which he had to wrestle. First Corinthians 9:1-3 is an example: Paul insists to the Church that he was commissioned by Christ (others include Romans 1:5; 1 Corinthians 1:1-2; 2 Corinthians 1:1; Galatians 1:1). Some even believe that 2 Corinthians 11:26 suggests that there was a plot to murder Paul; a plot formed by other Christians.
Such combined opposition—lost humanity, spiritual adversaries, and distrusting fellow Christians — must have caused Paul to despair, with evidence in his writings that he carried out his missionary work with the prospect of martyrdom before his eyes (Philippians 2:17), which ultimately turned out to be true. Paul was beheaded, tradition asserts, under the persecution of Nero near the third milestone on the Ostian Way. Constantine built a small basilica in Paul’s honour by AD 324, which was discovered in 1835 during excavations preceding the erection of the present basilica. On one of the floors was found the inscription PAVLO APOSTOLO MART – “To Paul, apostle and martyr”.
Paul’s 180 degree turnaround from his Pharisaic life is not disputed by any learned scholar of history, either secular or Christian. The only question is: what caused his about-face? What would cause a very learned Jewish Pharisee to suddenly embrace the very movement he violently opposed and be so committed to it that he would die a martyr’s death? The answer is found in Galatians 1:13-24:
“For you have heard of my former manner of life in Judaism, how I used to persecute the church of God beyond measure and tried to destroy it; and I was advancing in Judaism beyond many of my contemporaries among my countrymen, being more extremely zealous for my ancestral traditions. But when God, who had set me apart even from my mother’s womb and called me through His grace, was pleased to reveal His Son in me so that I might preach Him among the Gentiles, I did not immediately consult with flesh and blood, nor did I go up to Jerusalem to those who were apostles before me; but I went away to Arabia, and returned once more to Damascus. Then three years later I went up to Jerusalem to become acquainted with Cephas, and stayed with him fifteen days. But I did not see any other of the apostles except James, the Lord’s brother. (Now in what I am writing to you, I assure you before God that I am not lying.) Then I went into the regions of Syria and Cilicia. I was still unknown by sight to the churches of Judea which were in Christ; but only, they kept hearing, ‘He who once persecuted us is now preaching the faith which he once tried to destroy.’ And they were glorifying God because of me"
There are still people today who denounce Paul and challenge his authority. Of all the apostles, Paul surely faced the worst hostility, yet right up until his death, he was a forthright advocate for Christianity, and preached the gospel of Christ without apology or excuse.