According to the orthodox faith, the rebirth of man is realised with the holy baptism. This is not the baptism that John would conduct, for that is differentiated from the christian baptism (Acts 19:3-5). The christian baptism is conducted in the name of the Father and of the Son and of the Holy Spirit (Matt. 28: 19).
With the Christian baptism, one wears Christ, receives the Spirit of adoption and becomes heir of God and co-heir of Jesus Christ (Gal. 3: 26-29. Rom. 8: 17). The holy Bible assures us that there are no two baptisms for the faithful; the baptism with water that is followed by holy chrismation, is the "rebirth from above" of John 3: 3-5.
Therefore, the Christian baptism is necessary for salvation (Mark 16: 16. 1 Peter 3: 20-21). With this, we die in relation to sin and become reborn spiritually (Acts 2: 38. Rom. 6: 1-11. Titus 3: 5). With the holy baptism we receive the Spirit of adoption and become "children of God" (Rom. 8: 5-11. Gal. 4: 5-6), for with baptism we become part of the body of the Lord, the Church (Acts 2: 41.47. 1 Corinth. 12: 13. Gal. 3: 26-28); "one body and one Spirit...one faith, one baptism" (Eph. 4: 4-5). The Church, who is "the pillar and ground of the truth" (1 Tim. 3: 15), interpreted the John 3: 3-5 in reference to the holy baptism.
St. Justin (d. 165) connects the baptism with the "rebirth" of the John 3:3-5 ; in fact he calls it "way of rebirth" (Apol. 1: 61). Origen (185-254) says that the Holy Spirit exists "only to those that receive it via baptism" (by Athan. To Serap. epistle 4, 10). Tertullian (d. 220) mentions "without the baptism the salvation belongs to no one, exactly because of the word of the Lord 'if someone is not reborn from water does not have the life'" (On baptism, 12). Athanasios the Great (295-373) mentions that the person that gets baptised "gets rid of the old self, renovates himself above, reborn in the grace of the Spirit" (To Therap., epistle 4, 13).
But in the time of the great fathers as well, the Church interpreted the words of the Bible in the same way, identifying the salvation and the rebirth with the baptism.
St. John Chrysostom is mentioned in the conversation with Nicodemos (John 3: 1-21) and calls the baptism "λοχείαν", i.e. giving birth, and "new way of creation...from water and Spirit"; "and if someone is asked 'how come from water?', then the answer that must be given is: 'in the same way that in the beginning the first subjective element was soil and everything was the work of the Creator, this way now too, the water is the subjective element, and everything is the work of the grace of the Spirit'" (Chrys., To Jo., speech 25, 2).
"For nothing perceivable was handed over to us by Jesus; but with perceivable things, all of them however conceivable. This is also the way with the baptism; the gift of the water is done with a perceivable thing, but the things being conducted, i.e. the rebirth and renovation, are conceivable. For, if you were without a body, He would hand over these bodiless gifts as naked [gifts] to you. But because the soul is closely linked to the body, He hands over the perceivable ones to you with conceivable things " (Chrys. to Matt., speech 82, 4).
St. Gregory the Theologian (381) mentions three births: "the body's, the one via the baptism and the one via the resurrection" (Speech 40: 2, To the holy baptism).
But the fathers of the Western Church as well, like Blessed Augustine, name the baptism "mystery of rebirth". For this reason, whoever denies nepiobaptism, finds himself opposed to the holy Bible, but also to the "convention of the Church, who was given from the old days and has always been kept" (August. epistle to Sixto VII 32. X 43).
The event of the identification of the baptism with the rebirth does not of course mean that the baptism delivers us from the personal battle for the upkeeping and its giving fruit, of the spiritual gift. On the contrary, the Church wishes that the Lord proves the neophotistos an "unbeatable fighter against the ones that show enmity to him" and to give him the enlightenment of "always studying within Your law and doing the things that are liked by You".
As it has been mentioned above, the baptism makes us "wear" Christ and enters us into the Body of Christ, that is in the "kingdom of God" (John 3: 3-5); but this is the "engagement" (2 Corinth. 5: 5. Eph. 1: 14), that man can lose. After all the period of engagement, even in human relationships, is a period of trial. For this reason exercise and struggle are required (1 Thessalonians 5: 6-11. 1 Peter 5: 8-9).
EXPLANATION OF TERMS USED IN THE CHAPTER
Chrysostom = name added to one of the three Hierarchs, John (Basil the Great and Gregory the Theologian are the other two), meaning "having a golden mouth". John Chrysostom's Liturgy is conducted in Orthodox Churches around the globe every Sunday. Basil the Great also wrote a Liturgy which is still conducted a few times a year; it is essentially the same as Chrysostom's, whose Liturgy is an abridged version of St. Basil's. Both Liturgies are essentially identical apart from some non-sacramental prayers, and both stem from St. James' Liturgy. In all three ones (including a fourth one by St. Mark the Evangelist which is still conducted in Alexandria, Egypt, stemming again directly from St. James' one) we notice that the sacramental parts are identical. These cannot be changed for they were told by our Lord to us, so that we know exactly how to conduct the Sacrament of Eucharist, the whole setting of the remembrance of the life and crucifixion of our Lord etc. For this reason these Liturgies are called divine Liturgies.
mysteries = A mystery in the orthodox faith refers to the transmission of the invisible divine grace via visible signs. For instance, what the Roman Catholics call "the seven sacraments" are all mysteries, as well as the nativity of the Son from the Father and the procession of the Spirit from the Father and His mission from the Son are all mysteries. For more on this subject, visit this link.
nepiobaptism = the baptism of infants. (Also, nepios = the one to whom reasoning has not been developed yet (male structure). nepion = same thing, but male or female (neuter structure) ; nepia = plural of nepion.)
neophotistos = neos ( = new) + photizo (= to light) = recently enlightened one; neophotisti is the plural.
engagement = the association with the human period of engagement, a trial period before marriage, is the reason why I use this word more than "earnest" as is mentioned in the translated KJV Bible (for in Greek the two words coincide). So engagement as in a "before marriage" notion; not an "engaged in an activity" notion or something.