New Defender's Study Bible Notes
3:3 born again. The vital doctrine of regeneration, or the new birth, has been applicable in all ages, for man by nature is a lost sinner, and must be reborn spiritually through faith in God and His promises if he is to be saved. Note, for example, such Old Testament Scriptures as Isaiah 1:18; Psalm 51:10; Ezekiel 18:31. Nevertheless, this vital doctrine is crystallized and clarified and individualized more in the New Testament, especially in this chapter. See also II Corinthians 5:17; Galatians 6:15; Colossians 3:10; Titus 3:5; I Peter 1:23; and other New Testament verses on the new birth.
3:3 kingdom of God. Because of the preaching of John the Baptist that “the kingdom of God is at hand” (e.g., Mark 1:15), Nicodemus had undoubtedly been studying the Biblical promises of the kingdom—perhaps such passages as Isaiah 9:6-7; Zechariah 14:9; Daniel 7:13-14; Psalm 72:1, 7-11; as well as others. But now he is surprised to hear Jesus say that one cannot even see that kingdom without being born again!
3:5 of water and of the spirit. “Water and the Spirit” here has the connotation of “water, even the Spirit.” The death and rebirth illustrated by John’s baptism, in which Nicodemus and his colleagues on the council had been so interested (John 1:25) was merely symbolic of rebirth in the Spirit. Some expositors have equated the “water” here with the Word and others have taken it to mean the water in the mother’s womb, but the context surely refers to baptism, and that is certainly what Nicodemus would have understood it to mean. The essential conclusion of Christ’s reply was that regeneration by the Holy Spirit was prerequisite to entering the kingdom of God. Paul used the same baptismal figure of the new life in Romans 6:4 and called it “the washing of regeneration” in Titus 3:5.