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 10:3-6
"For though we walk in the flesh, we do not war after the flesh: (for the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds;) casting down imaginations, and every high thing that exalteth itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ; and having in a readiness to revenge all disobedience, when your obedience is fulfilled"