Paul begins to teach the Corinthians by emphasizing a truth that they already know. "I want to remind you that ... her." (See: [[rc://en/ta/man/translate/figs-rquestion]])
This can also be stated in active form. Alternate translation: "when a man joins his body to the body of a prostitute, it is as if their bodies become one body" (See: [[rc://en/ta/man/translate/figs-activepassive]])