24 Know ye not that they which run in a race run all, but one receiveth the prize? So run, that ye may obtain.Yes, even Paul recognized that he could be cast out (of the kingdom of God) if he did not keep his body under subjection.
25 And every man that striveth for the mastery is temperate in all things. Now they do it to obtain a corruptible crown; but we an incorruptible.
26 I therefore so run, not as uncertainly; so fight I, not as one that beateth the air:
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.
This may seem odd or even harsh, until one observes the catastrophe that lack of self-control often brings. Inability to control one's temper leads to frequent harm to others; those who are captive to lust tend to become caught up in immorality or at least become deaf to the Spirit, their lives becoming a spiritual wasteland even if they don't commit adultery or become deviant; inability to control the tongue leads to great devastation through gossip; and those who cannot control other appetites become, at a minimum, less able to serve God through their captivity to the flesh.
May we seek the guidance of the Spirit in our lives to be able to follow Paul's teachings on gaining mastery over the flesh, that we not be castaways ourselves.
By the way, the passage from 1 Cor. 9 is also one of many passages from Paul showing that some modern Protestant doctrines really need to be reconsidered in light of the Bible. If Paul was concerned about becoming a castaway and said the we all need to run to obtain the prize, how can we accept the idea of "irresistible grace" in which those who God chooses to save are saved no matter what, or the idea that once we choose Christ God cannot let go of us? Paul's paradigm is much more consistent with the LDS view of salvation by grace offered to us in a covenant, in which we must keep the terms of the covenant to gain access to that grace. Effort in striving to follow God and keep His commandments does nothing to save us or "earn" salvation, but is required under the terms of His generous covenant (and is an expression of our faith in Christ): we are to follow Christ, keep His commandments, repent of our many sins, and through His Atonement gain access to the infinite grace He offers us unworthy creatures. And of course, in all of this, we have free agency - freedom to choose Christ, and freedom to reject Him, and that freedom to reject is not taken away once we move toward Him. For this reason, it is no surprise that a few verses later Paul said, "Wherefore let him that thinketh he standeth take heed lest he fall" (1 Cor. 10:12). Yes, we can fall - anytime - if we are not cautious. Gaining self-control over our bodies is one of the things we need to do to keep ourselves from falling.