…a thorn was given me in the flesh, a messenger of Satan to harass me, to keep me from becoming conceited. Three times I pleaded with the Lord about this, that it should leave me. But he said to me, “My grace is sufficient for you, for my power is made perfect in weakness.” (2 Corinthians 12:7-9 ESV)
How can one be strong in weakness?
At the core of the Apostle Paul’s Second Letter to the Church at Corinth is a paradox. Christ was crucified in weakness, but in his weakness displayed the power of God (13:4). This same paradox was displayed in Paul’s private pain (12:7-9) and his very public humiliation as he writes:
We are afflicted in every way, but not crushed; perplexed, but not driven to despair; persecuted, but not forsaken; struck down, but not destroyed; always carrying in the body the death of Jesus, so that the life of Jesus may also be manifested in our bodies. (4:8-10)
This paradox manifests itself in that when we find ourselves at the end of our rope, we abandon our private idolatries and turn to the living God who is our only real hope. Paul writes: to this day whenever Moses is read a veil lies over [our] hearts. But when one turns to the Lord, the veil is removed. (3:15-17) Herein lies the paradox, that our own strength (for the Israelites, the law) veils the presence of God in our lives.
Second Corinthians is a very personal and complex letter. For example, Paul provides two separate lists (6:4-10 and 11:23-29) of own afflictions—who brags about being beaten and thrown in prison? He is writing from Macedonia (9:2) around 56 AD just before his final journey to Jerusalem. Theological topics addressed include: the character of God, salvation, the Gospel, the church, the nature of apostleship, Christian ministry, the Christian life, suffering, stewardship, Satan, and eschatology (Harris 2005, 105, 114-125).
The importance of Second Corinthians in the life of the church is underscored by the attention given to even small portions of this letter. For example, The Confession of 1967  adopted by the Presbyterian Church (USA) emphasizes these verses:
All this is from God, who through Christ reconciled us to himself and gave us the ministry of reconciliation; that is, in Christ God was reconciling the world to himself, not counting their trespasses against them, and entrusting to us the message of reconciliation. Therefore, we are ambassadors for Christ, God making his appeal through us. We implore you on behalf of Christ, be reconciled to God. (5:18-20)
Paul’s emphasis is on reconciling the world to Christ; the Confession expands on this idea to speak about reconciling the church to divergent groups in society.
Garland, David E. 1999. 2 Corinthians: An Exegetical and Theological Exposition of Holy Scripture. New American Commentary. Nashville: Holman Publishing.
Hafemann, Scott J. 2000. The NIV Application Commentary: 2 Corinthians. Grand Rapids: Zondervan.
Harris, Murray J. 2005. The Second Epistle to the Corinthians: A Commentary on the Greek Text. NIGTC. Grand Rapids: Eerdman.