Note 1 at 1Co 9:16: The word "necessary," as defined by the American Heritage Dictionary, means "required by obligation, compulsion, or convention." Paul was referring to the fact that the Lord compelled him to become a preacher of the Gospel. Paul had fought against the Lord's conviction (see note 6 at Ac 9:5), and it was only through his dramatic encounter with the Lord on the road to Damascus that Paul yielded.

We can only speculate what would have happened to Paul if he had not yielded to the Lord at that time, but from his continued statement in this verse, it is clear that Paul perceived there would have been great loss if he had refused.