Will you be found worthy or wanting?
But I keep under my body, and bring it into subjection: lest that by any means, when I have preached to others, I myself should be a castaway. (1 Corinthians 9:27 KJV)
Paul was constantly reminding himself to practice what he preached! This is spiritual discipline at its best! Paul understood foremost that it was not a good representation for the Gospel, and secondly towards other people, to preach one way of living towards others, but in the shadows choosing to live in a different spiritual fashion not honoring to God or worthy of His fellowship in the eternal realm.
Paul understood the spiritual role model he set forth in this world has many watching him closely. Some choosing to tear apart his example bit by bit to further examine exactly what he was made of. Any part of his life that did not measure up to the standards God set forth would be used as a strike against God first, and secondly against Paul, rather than being useful in furthering the gospel message.
Paul desired to be found faithful, shining a light for others, and even more importantly found in good fellowship with God rather than exiled in the flames of Hell for all eternity without His presence.