At least every mainstream Christian knows that to be saved one must be born again. Jesus says: “Truly, truly, I say to you, unless one is born again, he cannot see the kingdom of God” (John 3:3).
The problem isn’t believing what Christ says, the problem is understanding what this means. For the Catholic being “Born again” refers chiefly to the transforming grace of God received at baptism; it refers to the continuous work of the Spirit in his soul. However, to the Protestant it often refers to something entirely different, it refers at least to a moment of emotio-psychological overflow ideally after hearing a minister deliver a sermon and inviting everyone to become born again probably by standing up and saying a few prayers. At this time the listener is invited to make a decision and after the prayers becomes “born again”, even though this person had already been baptized.
Being born again means being regenerated, to be brought from the death of sin to the life of grace in Christ; to be justified and be set free from the slavery of sin, to have the power of adopted sons, and the pledge of eternal life.
St Paul links this regeneration or being reborn with baptism:
6 What shall we say then? Are we to continue in sin that grace may abound? 2 By no means! How can we who died to sin still live in it? 3 Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? 4 We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. Rom. 6:1–22
The Greek phrase “gennatha anothen” is what is usually translated “born again” and it occurs twice in the Bible (John 3:3 and 3:7). And this is a questionable translation not accepted by some scholars. This is because the Greek word “anothen” though sometimes translated “again”, is mostly translated in the NT as “from above”. So you find some translations saying “born again” and others saying “born from above”.
The effects of baptism is important to consider. The sacrament of baptism confers grace, and this is a gift of God; his initiative. He is always the one to utter the call, ours is to respond by accepting. The work of regeneration or rebirth isn’t through the initiative of men, but by the action of God; by the action of his Spirit.
4 Nicodemus said to Him, "How can a man be born when he is old? He cannot enter a second time into his mother's womb and be born, can he?" 5Jesus answered, "Truly, truly, I say to you, unless one is born of water and the Spirit he cannot enter into the kingdom of God. 6"That which is born of the flesh is flesh, and that which is born of the Spirit is spirit (John 3:4-6)
What the Church understands from the teachings of Christ and the Apostles is that being “reborn” is to be regenerated through the waters of baptism, as St Peter compared being “saved by water” in reference to Noah and the ark (1 Pet. 3:20–21), and as Christ assures being born of “water and spirit”, all are in reference to baptism and the reception of the Holy Spirit who comes from above. The crux of the matter is we know to be saved we must be reborn, the problem is what this rebirth means. We cannot be saved by our own power, it must be God’s gift. If what we have does not come from above, we cannot be saved. Christ came from above to redeem us, so he sent the Holy Spirit from above to confirm us and make us Sons. If we do not have the Spirit of God in us, we cannot be saved; if we have not been baptized we cannot receive the Spirit.
Peter said to them, "Repent, and each of you be baptized in the name of Jesus Christ for the forgiveness of your sins; and you will receive the gift of the Holy Spirit. ACTS 2:38
It is finally the Lord’s Spirit who grants us freedom, adopts us, unites us in the Body of Christ, and gives us eternal life.