1 Corinthians 9:25-27

²⁵ Now every athlete who goes into training conducts himself temperately and restricts himself in all things. They do it to win a wreath that will soon wither, but we [do it to receive a crown of eternal blessedness] that cannot wither.

²⁶ Therefore I do not run uncertainly (without definite aim). I do not box like one beating the air and striking without an adversary.

²⁷ But [like a boxer] I buffet my body [handle it roughly, discipline it by hardships] and subdue it, for fear that after proclaiming to others the Gospel and things pertaining to it, I myself should become unfit [not stand the test, be unapproved and rejected as a counterfeit].