
There is no reason to believe that Paul's thorn in the flesh was 
a sin in his life.  That makes little sense in the light of Paul'
writings taken in totality.  He writes of how he presses for the
mark, and keeps his body submitted.  No doubt Paul had to struggle
with the flesh just like every Christian.  Paul does associate his 
thorn with a Satanic messenger, and with physical infirmities and tribulation,
but not with a sin in his life.