2 Corinthians 6:3-10

The Corinthians were being pressed to request external evidence of true apostleship: letters of commendation and religious credentials from Paul.
Paul encouraged them to look upon the heart. Nevertheless, Paul could point to external evidence that marked one as a true apostle, minister and ambassador of Christ. His list is probably not what they were expecting. Every outward difficulty that Paul encountered was met with an inner strength that came through the power of the indwelling Holy Spirit. It is the same for every believer.