The book of 2nd Corinthians is a Pauline Epistle (letter from Paul). The Apostle Paul wrote it about 56 A.D. The key personalities of this book are the Apostle Paul, Timothy, and Titus. Paul wrote this letter to the church in Corinth to defend and protect his Apostleship, and to teach and warn against false teachers who were spreading heresy.The last thing Apostle Paul teaches in 2nd Corinthians is how to test yourself. If you want to know if you are a Christian, if you want to know if you are a believer and follower of Jesus Christ, than you must test yourself, "to see if you are in the faith"; examine yourself with Scripture (13:5).