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)
Paul wrote two letters to Christians in Corinth, a city that was given to sexual immorality and lewd behaviors. The imagery that Paul used in 1 Corinthians 9:27 is strong and purposeful.

He wrote: “I keep under my body.” Notice the first word in the sentence: I. Paul did not say, “Now that I’m saved, God keeps me from sinning with my body.” No, Paul said this is something that God had given him the ability and authority to control. Paul was the one who put his body in check.
Paul also wrote that he brought it into subjection. Keeping your body is making sure that it is entirely under your control. Bringing it into subjection refers to situations when your body wants to act against your spirit. Still, instead, you force it back to where it knows that the real you, your spirit, is in charge.
There is no difference between sin today and sin in the first century. The opportunity for the flesh to sin has been around since the Garden of Eden. Technology may change, but men do not. Temptations remain the same, but access to them has become much more prevalent.
Paul's call to keep our body under and bring it into subjection is something every believer must adhere to. Otherwise, your body will have mastery over your life, leading you away from God’s best.
Practical Application – Every morning, you should tell your body that it is under the power of your spirit. Speak to your flesh and tell it to get in line. Make a serious decision to put it in order before you walk out the door.
Galatians 5:13; Galatians 5:24