1 Corinthians 15:31

I protest by your rejoicing which I have in Christ Jesus our Lord, I die daily. (KJV)

Then: Corinthians probably understood "I protest" to mean "I swear" (Baker, p. 224). Paul wanted them to know of his pride in them. He feels able to boast about their faith and Christ's work in thier lives. What Paul intended the Corinthians to understand through his phrase, "I die daily," is subject to a lot of explanations. John Calvin presents it as a "contempt of death" because of the ever present formidable dangers to his life.

Now: To "die daily for Christ" is an oft preached phrase taken from Paul's ministry. The Wiersbe Bible Commentator states that here it does not mean the same as the theme of Romans 6 "dying to self." Instead it refers to physical dangers(p.494). Baker (p.228) feels that Paul means the slow wearing out of his physical body.

Extra Source: Cornerstone Biblical Commentary 1 Corinthians (William Baker), 2 Corinthians (Ralph Martin & Carl Toney), ed. by Philip Comfort. Carol Stream: Tyndale House Publishers, c2006.
Commentaries on the Epistles of Paul the Apostle to the Corinthians by John Calvin translated from the Original Latin, and Collated with the Author's French Version by the Rev. John Pringle, Volume one from the Calvin Translation Society edition and downloaded from the Christian Classics Ethereal Library on line at http://www.biblestudyguide.org/comment/calvin/comm_vol40/htm/i.iv.htm
Wiersbe Bible Commentary The Complete New Testament by Warren W. Wiersbe (Colorado Springs CO: David C. Cook, c2007) http://books.google.com/books?id=Sn18qwyJw9QC&pg=PA453&lpg=PA453&dq=1+Corinthians+15+commentary&source=bl&ots=uEH6xD4cBX&sig=O-Yucl21olPnNQo8wDjVu1LTrs4&hl=en&ei=pzcJS_igCZHTlAe9t4mFBA&sa=X&oi=book_result&ct=result&resnum=4&ved=0CBEQ6AEwAzhk#v=onepage&q=1%20Corinthians%2015%20commentary&f=false