A rhetorical question with the answer included in the question. Alternate translation: "For if a man finds his enemy, he will not let him go safely." (See: [[rc://en/ta/man/translate/figs-rquestion]])
Where Saul had believed David was his enemy, he learns that even though David will be king, David will not take over the throne from Saul by force, but will wait for Yahweh's appointed time.