It's an understatement to surmise that we can learn much from the life of Paul.  Of course, it is quite true no matter how understated it may seem.  Through his letters we find the man, the servant of the Lord, teaching, encouraging, admonishing and praising.  He's a man whose past would offend some and be admired by others:

"If anyone else thinks he has reasons to put confidence in the flesh, I have more; circumcised on the eighth day, of the people of Israel, of the tribe of Benjamin, a Hebrew of Hebrews; in regard to the law, a Pharisee; as for zeal, persecuting the church; as for legalistic righteousness, faultless."  Philippians 3:4b-6

God used Paul's past to make his future effective.  He transformed a sinner condemned into a sinner redeemed.  This sinner, this man who persecuted the church began to preach the gospel of Jesus Christ with such fervor and passion.  In the midst of sharing the "good news" he realized that young believers would need support and encouragement.  When God deemed, he journeyed to these young churches and when he was unable to go, he wrote to them.  The letter Paul writes to the Philippians is one not only of teaching but of great encouragement.  Despite his imprisonment, he lifted his fellow brothers and sisters up in prayer.  He wrote to them uplifting messages and displayed a faith most of us wonder would we display under such circumstances.

"...for I have learned to be content whatever the circumstances. I know what it is to be in need, and I know what it is to have plenty. I have learned the secret of being content in any and every situation, whether well fed or hungry, whether living in plenty or in want. I can do everything through him who gives me strength."  Philippians 4:11b-13

In the midst of chains, he offers encouragement to the church at Philippi.  He also used this letter to witness to any unbelievers who may read or hear it.  It is quite apparent that his eyes were fixed on one thing:

And what have we already attained?  As believers we have salvation through Christ!  We have become children of the KING!  We have attained royalty, but not through anything we've done; No, through the grace and mercy of God, through the sacrifice of His Son.  So, we should press on toward the goal being mindful that God has a purpose for us in this crooked world.  If we let Him, God can bring beauty in ashes, strength in weakness, honor in shame and freedom in chains.

“Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things.”
Philippians 4:8