Paul of Tarsus was the self-proclaimed "13th Apostle". He alone wrote nearly half of the New Testament. His work consists of 13 letters (or "epistles") to various Christian communities during the middle part of the 1st century.
The epistles are arranged into three parts in the New Testament canon.
The first part consists of nine epistles to seven church congregations: 1. Romans; 2. First Corinthians; 3. Second Corinthians; 4. Galatians; 5. Ephesians; 6. Philippians; 7. Colossians; 8. First Thessalonians; and 9. Second Thessalonians.
The second part consists of one general letter, the Book of Hebrews. The third part consists of three pastoral letters to Timothy, Titus, and Philemon, who were pastors of early Christian churches.
Four of Paul's letters (Colossians, Philemon, Ephesians and Philippians) were written while Paul was under house arrest in Rome during 60-61 AD.
It is interesting to note that Paul did not know he was writing "scripture" when he was writing his letters. As far as he knew, he was just writing letters to pastors and congregations. Paul's letters eventually were recognized as the the earliest scripture by future leaders and councils of the Catholic Church. They, along with the four canonical Gospels, became the primary basis for the New Testament.
What is fascinating is to see how often Paul's letters are quoted to justify theological positions and how seldom Paul is given direct credit by saying... "According to the apostle Paul...". What usually happens is that people will attribute quotes from Paul's letters by saying... "According to scripture... " or "According to God's Word... ".
Another method of attribution is to simply use the name of the particular pastor or community to whom Paul's letter was directed... "According to First Corinthians... "According to the Book of Colossians... ". The effect is powerful and carries more authority than saying... "The apostle Paul said... ". If you were to just say... "According to Paul... " over and over again instead of attributing quotes to the various pastors and communities, eventually people would start to wonder... "Who the heck was this Paul fella anyway and why should I believe him?" After all, wasn't Paul a human being living in the 1st century, with the same faults, guilts and weaknesses as anyone else?
Much of Paul writing suggests that he, along with many other early Christians, was expecting Jesus to return his (Paul's) lifetime to establish the Kingdom of God on earth... in other words, the Messiah would return to free Israel from Roman occupation. It didn't quite happen the way Paul had envisioned.
Paul may have been inspired, but why take his word over more contemporary thinkers and writers that make more sense? Or over your own inspiration from God?
Nearly half of the Bible was written by ONE guy, who didn't even know Jesus personally.