What is a necessary component of being used by God to fulfill his purposes on this earth?  Difficulty, leading to humility.  And it almost goes without saying that for an apostle of Jesus Christ, it would take massive humility to be able to be used to that kind of extent and NOT fall away from being a useful vessel of the Lord into a life of self-exaltation.  We saw that humility in Saul in Eph. 3:1-8, but how does one arrive at that kind of self-assessment?  We can find the answer in 2 Cor. 4:7 But we have this treasure in jars of clay, to show that the surpassing power belongs to God and not to us. 8 We are afflicted in every way, but not crushed; perplexed, but not driven to despair; 9 persecuted, but not forsaken; struck down, but not destroyed; 10 always carrying in the body the death of Jesus, so that the life of Jesus may also be manifested in our bodies. 11 For we who live are always being given over to death for Jesus’ sake, so that the life of Jesus also may be manifested in our mortal flesh. 12 So death is at work in us, but life in you.
Humility is gained by being afflicted, perplexed and persecuted.  Otherwise, we might be tempted to think that the surpassing power of gospel ministry belongs to us and not God.  When we are bringing this treasure of the good news to others, God is often pleased to accompany our efforts with supernatural power.  That’s why we must be humbled.