That which is born of the flesh is flesh. That which is born of the Spirit is spirit.
The previous verse revealed the two elements of the new birth, this the requirement that both flesh and spirit participate in it.  Thus, what Jesus was saying to Nicodemus was: "Do what my disciples have done; first submit to John's baptism, and then come join my company."[12]  If he had done so, the second element of the new birth, the reception of the Spirit would have been completed after Pentecost.  The fact that at that particular time, Nicodemus could not have received the Holy Spirit, since he was not given yet, proves that the new birth as experienced in the new dispensation was in view here.  See under  John 7:39.