Nicodemus asserts that the miracles they have seen Jesus perform have been persuasive. Yet apparently not completely so. It's night after all.
After being asked about how anybody can have a second birth, Jesus answers him by asserting the necessity of the Spirit.
"What is born of the Spirit is spirit....The wind blows where it chooses..." Remember that the Greek word translated as wind also means breath or spirit. God breathes on us; a force moves us like the wind moves us and that force is as invisible as the wind as it is as potent as the wind.
"So it is with everyone who is born of the Spirit." Who is this "everyone"? Who has been born of the Spirit? Am I reassured? insulted? puzzled? grateful?