Paul's Experience, "l am going to boast only about how weak I am and how great God is to use such weakness for his glory.... The experiences I had [of being taken up to Heaven] were so tremendous, God was afraid I might be puffed up [full of pride] by them; so I was given a thorn in the flesh, a messenger from Satan to hurt and bother me, and prick my pride. "Three times I begged God to take it away. Each time he said, 'No. My grace [enablement] is adequate for you. My power [strength] shows up best in weak people. ' .. Since I know it is all for Christ's good, I am quite happy about 'the thorn, ' and about insults and hardships, persecutions and difficulties; for when I am weak, then I am strong — the less I have, the more I depend on him" (2CoT 12:5,7-10 tib). Paul teaches us several important lessons about tests and trials in the life of a leader. Among them are: 

Beware Of Pride. Valid spiritual experiences during times of prayer can cause us to be prideful.

Depend On God. Our discomfort is less important to God than our character. If our pride needs to be pricked, God will send along a messenger of Satan to make us weak, so we will depend on Him,

Rejoice In Trials. Only through humility and weakness can God's power be manifest in our lives. Hence, we can rejoice in tribulation, hardships and persecution, because we know it can result in God's power and glory being revealed in us. When we start seeking for the power, the glory and the life of the Spirit to be expressed through us, God's response to our petition does not come in the way we expect. We pray for patience, and He sends tribulation. Why? Because "tribulation develops patience " (Rom 5:3). He is answering our prayer, but not the way we thought He would. We must recognize that the buffeting may be "God... working in us to will and to do of his good pleasure "(Phil 2:13).

Affliction Separates The Chosen From The Called "I have chosen thee in the furnace of affliction" (Isa 48:10). In this verse, the word "chosen" is used in the sense of being "graded," as in a school course examination or test.
When we do our lessons and take our tests in school, we are "graded" by the teacher on how well we have performed. If we receive a passing grade, we graduate to the next level or grade, one that is more difficult and challenging.
How does God determine whether to give me a passing grade? He tests our  performance in the furnace of affliction. our  response to trials and frustrations is graded. God observes how  we react to heavy pressure and difficult, situations. If we  respond appropriately He says, "Well done, My good and faithful servant. Now you are ready to pass on to the next course, the next level of difficulty."

As we learn and grow. He presents us with ever harder tasks and continues to test, to grade, to choose. ' 'Many are called but few are chosen ' ' (Matt 20:16). Why are few chosen? Because we are graded in the furnace of affliction, and few of us pass the test for leadership. There is a powerful statement in the Book of Revelation concerning those the Lord Jesus allows to go forth in conquest with Him. "These shall make war with... the Lord of lords and the King of kings and they that are with him are called, and chosen, and faithful ' '(Rev 17:14). Three requirements were essential. You had first to be called, then chosen, and to have proved yourself faithful. Sufferings, trials and tribulations mark the path of those in this company. They've proven themselves worthy to be chosen and have stood faithful to the Lord, even if it meant hazarding their lives for Him.