John 3:10

And Jesus answered and said unto him, Art thou the teacher of Israel and understandest not these things?

By this answer, Christ did not deny some element of mystery regarding the questions Nicodemus had raised, but was exclaiming at his failure to understand the basic things Christ had commanded him to do. The Lord's words to this ruler of the Jews were the blunt equivalent of "Look, you Pharisees stop rejecting John's baptism; obey God by submitting to it; but that is only part of it; you must allow the Spirit of God to dwell in your heart, and that can come about only by your following me" (Luke 7:30).

Greater importance attaches to John's baptism than is usually supposed. Jesus submitted to that baptism, as did (presumably) all the apostles, for it is inconceivable that the disciples of Jesus would have refused a baptism to which Jesus himself submitted. Also, those disciples baptized others during John's ministry; and they could not have done this without themselves accepting it and obeying it. Though called the baptism of John, it was actually God's baptism administered by John. Also, for a season, it was also administered by Jesus through his apostles. It was mandatory for all Israel, even for the priests and Pharisees; and it was the only baptism in force until Pentecost. With Pentecost and the preaching of the Great Commission, John's baptism was supplanted by that of the commission; but it was valid until then. The function of John's baptism was exactly like that of the great commission in the particulars of its being by immersion and its being the separator between the true Israel of God and the hardened secular Israel with which the true Israel was commingled until Pentecost.

The Pharisees, including Nicodemus, had utterly rejected God's baptism administered by John, even though Jesus himself submitted to it; and that was the key to their ultimate rejection of Christ. The ignorance of the Pharisaical party regarding the sacred ordinance of baptism was the immediate beginning of the end of the whole Jewish nation as the covenant people. That stubborn blind ignorance, as it appeared so stark and adamant in Nicodemus, called forth the exclamation of Jesus in this verse. No wonder Israel was in trouble spiritually when even her noblest teachers rejected the idea of being born of water and of the Spirit. In such rejection, it was clear that the major part of Israel would continue to trust in Abrahamic descent, despite the warnings of both Jesus and John the Baptist (Matthew 3:8-10; John 8:39).

How strange is it that the same pattern of evil is endlessly repeated? Just as the Pharisees of Jesus' day stumbled at being "born of water," that is, at being baptized, just so, many today stumble at the very same thing; and it is no less a marvel now than it was then.