Jesus answered Nicodemus’s confusion by elaborating on the truth He introduced in verse 3: “Truly, truly, I say to you, unless one is born of water and the Spirit he cannot enter into the kingdom of God.” A number of interpretations have been offered to explain the phrase born of water. Some see two births here, one natural, and the other spiritual. Proponents of this view interpret the water as the amniotic fluid that flows from the womb just before childbirth. But it is not clear that the ancients described natural birth in that way. Further, the phrase born of water and the Spirit parallels the phrase “born again” in verse 3; thus, only one birth is in view. Others see in the phrase born of water a reference to baptism, either that of John the Baptist, or Christian baptism. But Nicodemus would not have understood Christian baptism (which did not yet exist) nor misunderstood John the Baptist’s baptism. Nor would Jesus have refrained from baptizing people (4:2) if baptism were necessary for salvation. Still others see the phrase as a reference to Jewish ceremonial washings, which being born of the Spirit transcends. However the two terms are not in contrast with each other, but combine to form a parallel with the phrase “born again” in verse 3. (For a careful examination of the various interpretations of born of water, see D. A. Carson, The Gospel According to John, The Pillar New Testament Commentary [Grand Rapids: Eerdmans, 1991], 191–96.)
Since Jesus expected Nicodemus to understand this truth (v. 10), it must have been something with which he was familiar. Water and Spirit often refer symbolically in the Old Testament to spiritual renewal and cleansing (cf. Num. 19:17–19; Isa. 4:4; 32:15; 44:3; 55:1; Joel 2:28–29; Zech. 13:1). In one of the most glorious passages in all of Scripture describing Israel’s restoration to the Lord by the new covenant, God said through Ezekiel,
For I will take you from the nations, gather you from all the lands and bring you into your own land. Then I will sprinkle clean water on you, and you will be clean; I will cleanse you from all your filthiness and from all your idols. Moreover, I will give you a new heart and put a new spirit within you; and I will remove the heart of stone from your flesh and give you a heart of flesh. I will put My Spirit within you and cause you to walk in My statutes, and you will be careful to observe My ordinances. (Ezek. 36:24–27)
It was surely this passage that Jesus had in mind, showing regeneration to be an Old Testament truth (cf. Deut. 30:6; Jer. 31:31–34; Ezek. 11:18–20) with which Nicodemus would have been acquainted. Against this Old Testament backdrop, Christ’s point was unmistakable: Without the spiritual washing of the soul, a cleansing accomplished only by the Holy Spirit (Titus 3:5) through the Word of God (Eph. 5:26), no one can enter God’s kingdom.
Jesus continued by further emphasizing that this spiritual cleansing is wholly a work of God, and not the result of human effort: “That which is born of the flesh is flesh, and that which is born of the Spirit is spirit.” Just as only human nature can beget human nature, so also only the Holy Spirit can effect spiritual transformation. The term flesh (sarx) here refers merely to human nature (as it does in 1:13–14); in this context, it does not have the negative moral connotation that it frequently does in Paul’s writings (e.g., Rom. 8:1–8, 12–13). Even if a physical rebirth were possible, it would produce only flesh. Thus, only the Spirit can produce the spiritual birth required for entrance into God’s kingdom. Regeneration is entirely His work, unaided by any human effort (cf. Rom. 3:25).
https://www.gty.org/library/bibleqn...t-does-it-mean-to-be-born-of-water-and-spirit
