John introduces Nicodemus with an unusually dense set of credentials. He is a Pharisee, a ruler of the Jews, and later is addressed as 'the teacher of Israel.' He comes to Jesus at night and respectfully calls him Rabbi.
The conversation therefore does not pit Jesus against an ignorant outsider but against the limits of an educated insider's understanding.
The Pharisees were an influential Jewish movement concerned with Torah and its interpretation. 'Ruler of the Jews' likely places Nicodemus among Jerusalem's recognized leadership, though the phrase alone should not be made to prove a particular office beyond the text. Calling him 'the teacher of Israel' emphasizes his standing as an instructor.
John does not explicitly say why he comes at night. Secrecy is possible, but John's recurring symbolism of light and darkness also makes the timing narratively suggestive.
Nicodemus' status makes Jesus' challenge sharper. Religious education, institutional standing, and recognition of miraculous signs do not by themselves produce the understanding Jesus demands.
John will return to Nicodemus later, allowing the reader to watch this cautious nighttime visitor move gradually into more public association with Jesus.