That means they did not dispute the miracles, the healings, the exorcisms. That’s astounding information. Jesus answers the question in Nicodemus’s heart by responding, “I tell you the truth, no one can see the kingdom of God unless he is born again.”
The expression "to be born again" (or literally, “to be born from above”) was in common usage among the Jews to indicate a conversion from Gentile to Jew, but they never used it in regard to someone who was already Jewish. Nicodemus is confused; this seems to be an absurd doctrine and so he mocks it by saying a man cannot enter his mother’s womb a second time.
Jesus clarifies it by explaining that a person must be born of water and the spirit, in other words, you must be born physically and spiritually. One cannot see the physical world until he is born. One cannot see the kingdom of heaven until he is born spiritually.
More about Nicodemus in parts 2 and 3.