A secondary aim is to show that Paul knew next to nothing about the Gospel stories, as he fails to mention them at crucial points and often seems to contradict them. Paul is often called the second greatest Christian who ever lived and the greatest evangelist who ever lived. He helped to spread the Gospel over a wide area. His letters are the earliest Christian documents we have. Paul's letters are pimary evidence.
Primary evidence is very important to historians.
For example, here is a coin from the time of Vespasian depicting the fall of Judea during the war between the Jews and Rome. Here is a coin from the time of Domitian. The letters 'Domitian' are clearly visible. There are 13 letters attributed to Paul in the New Testament. Romans and 1 Corinthians are very long and were written to teach people about the Gospel.