Nicodemus uses this question to emphasize that this cannot happen. Alternate translation: "A man certainly cannot be born again when he is old!" (See: [[rc://en/ta/man/jit/figs-rquestion]])
Nicodemus also uses this question to emphasize his belief that a second birth is impossible. "Certainly, he cannot enter a second time into his mother's womb! (See: [[rc://en/ta/man/jit/figs-rquestion]])