New Defender's Study Bible Notes
3:8 The wind. The only New Testament use of pneuma (meaning “spirit”) for “wind” is in this verse, although the Old Testament writers commonly used the same Hebrew word (ruach) for both “wind” and “spirit.” The reason for its unique use in this case is obviously to emphasize the similarity of the operation of the Holy Spirit to that of the wind. As the wind is invisible and gentle, so is the Spirit. And as the wind also exhibits great power on occasion, so does the Spirit (e.g., Acts 1:8).
3:8 so. As one cannot see the wind at work but can see its results, so it is with the new birth. It may come about slowly or suddenly, from one direction or another. One cannot detail the mechanics of the regeneration process. Just as one does not remember his physical birth, he may be unable to pinpoint his spiritual birth. As the proof of the one is the reality of his physical life, so the proof of the other is the reality of his spiritual life.