Jesus now explains what it means to be “born from above” (see on ch. 1:12, 13). The reference to “water” is a clear allusion to water baptism, which was administered to Jewish proselytes and was practiced by the Essenes (see pp. 63, 91).
Furthermore, for many months John had been baptizing his fellow Jews in the river Jordan (Matt. 3:5, 6, 11). Yet the Pharisees, who affected a superior degree of righteousness, refused baptism (Luke 7:30) because John made it the symbol of repentance (see on Matt. 3:6). Nicodemus had doubtless listened to John, and may have heard his statements about baptism with water (John 1:26) and with the Holy Ghost (v. 33). Nicodemus anticipated admission into the kingdom of God as a natural-born, devout Jew, but Jesus declared that anything less than a complete transformation of the life by the power of the Holy Spirit was inadequate. See on Rom. 6:3-6.
To be “born of water and of the Spirit” is equivalent to being “born again,” that is, “from above” (see on John 3:3). Those who are born from above have God as their Father and resemble Him in character (see 1 John 3:1-3; cf. John 8:39, 44). Hencefoth, they aspire, by the grace of Christ, to live above sin (Rom. 6:12-16) and do not yield their wills to commit sin (1 John 3:9; 5:18).