In this passage, Paul explains how he lives his life: strenuously for Christ. He begins by saying that he has not used his right to be supported by those to whom he ministers. Furthermore, he is not writing so that the Corinthians will support him, since it would be better to die than to lose this boast. The reason for this is that he has nothing to boast of when preaching the gospel because he must do it. On the other hand, he has a reward if he does it voluntarily, and not out of necessity. However, while doing it against his natural will, he has a stewardship of the gospel. However, he does have a reward: the boast that he preaches the gospel without using his right to support.
In verse 19, Paul explains that he does not accept support because he enslaves himself to everyone. In other words, he becomes like a Jew among Jews, like one under the Mosaic Law among those under it, like one without law among those without law, and like someone who is weak among those who are weak. He does this to everyone so that he can save them.
In verse 24, Paul illustrates this lifestyle with the example of someone running in a race: although everyone runs in the race, only one receives the prize. Therefore, he commands the Corinthians to run their lives so that they will win the race. Furthermore, everyone who competes in an athletic contest exercises self-control in their entire life. While they do it to receive a temporal reward, Christians do it to receive an eternal reward. Therefore, Paul concludes, he runs with an aim, and boxes with an aim by disciplining his body, and enslaving it, so that he will not fail to receive the imperishable wreath of the future life with Christ, or become disqualified.