In John 3, Jesus taught about two kinds of births:
1. Physical Birth (Birth "of flesh"): This refers to the natural birth we all experience as human beings. Jesus acknowledges Nicodemus' understanding of this birth when he says, "Very truly I tell you, no one can see the kingdom of God unless they are born again." (John 3:3) Nicodemus initially interprets "born again" literally, asking, "Surely no one can enter a second time into their mother’s womb to be born!" (John 3:4)
2. Spiritual Birth (Birth "of water and the Spirit"): This refers to a new birth that is necessary to enter the Kingdom of God. This birth comes from God and involves the Holy Spirit. Jesus explains, "Very truly I tell you, no one can enter the kingdom of God unless they are born of water and the Spirit. Flesh gives birth to flesh, but the Spirit gives birth to spirit." (John 3:5-6)
* "Born of water": This has been interpreted in different ways, including referring to baptism (a symbol of cleansing and new life) or to the natural process of childbirth (water breaking).
* "Born of the Spirit": This refers to the work of the Holy Spirit in a person's life, bringing about regeneration and a new relationship with God. It's a supernatural act of God that transforms a person's heart and mind.
In essence, Jesus is saying that physical birth is not enough. To truly see and enter the Kingdom of God, a person must also experience a spiritual birth, a new life brought about by the Holy Spirit.