1 Corinthians 9:27
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.
Note 16 at 1Co 9:27: No one can function on this planet without a body. It's our "earth suit." It's absolutely essential. However, it also is our biggest liability. If we let our physical senses dictate to us so that we live indulged lifestyles, the power of God will never be a constant characteristic of our lives. The flesh and the Spirit war against each other so that we cannot do the things that we would (Ga 5:17). We must "keep under" our bodies so the life of God can be manifest in us.
The phrase "keep under" in this verse comes from the Greek word "HUPOPIAZO," and this Greek word means "to hit under the eye (buffet or disable an antagonist as a pugilist), i.e. (figuratively) to tease or annoy (into compliance), subdue (one's passions)" (Strong's Concordance). Paul was drawing on the illustration of a boxer that he made in 1Co 9:26. His carnal self was the enemy, and he was beating it to death.
The phrase "bring it into subjection" comes from the Greek word "DOULAGOGEO," and this Greek word means "to be a slave-driver, i.e. to enslave (figuratively, subdue)" (Strong's Concordance). Paul was a slave driver to his flesh. The spirit man was in control. Why? Because it would have been possible for the Apostle Paul to be castaway (see note 17 at this verse) or lose part of his reward.
Jesus taught that prayer and fasting were two things that would break the control of the flesh over us (see note 4 at Mt 17:21).
Note 17 at 1Co 9:27: The English word "castaway" was translated from the Greek word "ADOKIMOS," and it means "unapproved, i.e. rejected; by implication, worthless (literally or morally)" (Strong's Concordance). This same word was translated "reprobate" three times (Ro 1:28, 2Ti 3:8, and Tit 1:16) and "rejected" once (Heb 6:8). Also, in 2Co 13:5-7, it was translated "reprobates" three times, once in each verse. Here, in 1Co 9:27, Paul was speaking of a loss of his salvation (see note 6 at Ro 1:28).