“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). In this letter, Paul was writing to the Corinthians. These Christians were having problems with thinking that the freedom they had in Christ allowed them to do things they should not do. They also thought that they did not need to consider what other Christians thought of their choices. They thought their freedom gave them the right to do what they wanted to do.
In Chapter Nine, Paul told them that the freedom in Christ did not give them the right to do anything they wanted to do. He said that he had the same freedom, but that he made choices based on whether it was allowed by Christ and whether it would offend others. If a choice would offend Christ or others, he did not choose it.
In the verse above, the words “keep under” come from a Greek word that was used to describe getting a black eye in the sport of boxing. Thus, Paul was stating that he was willing to mentally bruise and give a black eye to his body for the cause of Christ. It was better to hurt inside from not doing something one wanted to do than to offend Christ or another person.
Study your Bible. Obey Christ. Keep under your body for the cause of Christ. If any of this is hard to understand, ask an adult to help you.