The third of the Epistles is Paul's second letter to the Christians in Corinth, or II Corinthians. Some members of the Church in Corinth had challenged Paul's authority over them and so he had sent two of his followers, Titus and Timothy, ahead before setting off himself to Corinth. Titus returned from Corinth and reported to Paul that the Christians there had repented of their challenge to Paul's teaching. This heartened Paul, but there were still some issues which need dealing with, and so he wrote this second letter.
II Corinthians 3:15-18
"But even unto this day, when Moses is read, the vail is upon their heart. Nevertheless when it shall turn to the Lord, the vail shall be taken away. Now the Lord is that Spirit: and where the Spirit of the Lord is, there is liberty. But we all, with open face beholding as in a glass the glory of the Lord, are changed into the same image from glory to glory, even as by the Spirit of the Lord"