What is an Epistle?—One of the letters, written openly, adopted as books of the New Testament. Paul authored 7 canonized letters. These are the letters or epistles to Rome, Corinth, Galatia, Ephesus, Philippi, Colosse, and Thessalonica.
What is an Apostle?—Apostle (Gk. Apostolos). Envoy, ambassador, or messenger commissioned to carry out the instructions of the commissioning agent.
Who is Paul?—This is the former Saul of Tarsus, a Jewish Rabbi of the Jewish sect of law-keeping, brilliant-minded, hard-hearted Pharisees of which we read so much of in the gospels. We learn of this man called Saul in Acts chapter 7, a man filled with rage and hate for the Christians. He hated what was being preached, so much so that he consents to the death of the first Christian martyr, a young man named Stephen.