Paul continues his defense of his ministry against "false apostles." We don't know exactly what the "false apostles" were teaching or doing but there are some hints in this passage. The message of the gospel they are preaching (another Jesus) is different from what Paul is preaching. They appear to be "boastful" and greedy. Paul defends his humility and makes note that he did not burden the Corinthians in any way. He calls his opponents "deceitful (13) and under disguise comparing them to Satan himself who "disguises himself as an angel of light (14)." I remember an early lesson in life that it was important to weigh and evaluate every teaching. In the modern world there are "false apostles" who teach things that are contrary to the Gospel. Sometimes these preachers blend American capitalism with the Christian faith or they blend American political or historical experience with the Christian faith and end up preaching something that sounds like Christianity but is actually promoting something else. The prime examples of this are the "prosperity gospel" and "American civil religion." Both of these examples are dangerous because they draw people away from the challenge and expectation of the gospel.
Paul notes these challenges beginning in verse 16. As further evidence of his Apostleship, Paul does not cite his successes nor does he cite his victories (he is not boasting). Instead, Paul cites his sufferings and his hardships. He boasts that he is a Hebrew, a descendent of Abraham. That he has suffered greatly for the message of the gospel. Notice the list: imprisonment, floggings, (near death), beaten with rods, stoned, shipwrecked, in constant danger, pressure and anxious for the churches he has planted. This, apparently, was the life of the Apostle. It was not a glamorous and "powerful" position. It was a servants position. In order to preach the gospel and plant churches the Apostles had to endure great suffering, hardship and persecution. All of them, according to the best records of the time, were martyred. What a life of ease and comfort we modern preachers have in comparison! But, for Paul, this litany is evidence of his authenticity -- his claim and calling to be an Apostle.