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 13:1-4
"This is the third time I am coming to you. In the mouth of two or three witnesses shall every word be established. I told you before, and foretell you, as if I were present, the second time; and being absent now I write to them which heretofore have sinned, and to all other, that, if I come again, I will not spare: since ye seek a proof of Christ speaking in me, which to you-ward is not weak, but is mighty in you. For though he was crucified through weakness, yet he liveth by the power of God. For we also are weak in him, but we shall live with him by the power of God toward you"