Most people agree that Jesus is positive about the "being born again" requirement as recorded in John 3:3-8. "Verily, verily, I say to you." They will agree that the "new birth" precedes entering the Kingdom of God and Heaven itself (Matthew 16:18, Acts 14:22; 2 Peter 1 :11). Most will even concede that every one must be born of the Spirit. They will agree that the new birth produces radical changes (John 3:8). They generally will agree that whatever the "new birth" is, it is contained in the Great Commission (Matthew 28:19-20; Mark 16:15,16; Luke 24:45-47) and that which the apostles required of sinners include what the new birth is (Matthew 28:18-20).
However, three things that most people in the religious world do not agree on: (1) how the Spirit does His part; (2) what the "water" is and how one is born of it; and (3) what proof there is of one having the new birth.
First, we should know that the words spoken [and written] by the apostles and prophets were the words from Christ and God's Holy Spirit (John 16:13; 2 Timothy 3:16,17). "For it is not ye that speak, but the Spirit of your Father which speaketh in you," (Matthew 10:20). After Jesus ascended into Heaven, the 12 apostles were together (Acts 1:26) and Christ sent His Spirit to them from the Father (Luke 24:48). "And they were filled all together [spirit of holy], and they began to speak with other languages, as the Spirit gave to them to be declared" (Acts 2:4, ABPen - Apostolic Bible Polygot in English). The Word of God is the seed of the birth of the Spirit (John 3:3,5). Disciples were to "...receive the implanted word! the one being able to deliver your souls" (James 1:21b). The word that saves is "implanted" by the hearer (Greek emphutos- Thayer's- "inborn, implanted by ...others instruction." This word implanted meant basically "to germinate or grow in" (Michelson Enhanced Strong's). Faith in each new born Christian comes by "hearing and hearing by the Word of God" (Romans 10:17).
Second, what is the "water" and how is one born of it? If the new birth is contained in Jesus' Great Commission, is it not then the water baptism that's commanded there? Jesus commanded one to believe (hence, the Word of God is accepted by a true heart) and be baptized (Mark 16:16). Peter's Words from the Spirit required water baptism (Acts 2:38; Acts 10:48). Peter commanded water for Cornelius to be baptized. Saul of Tarsus had his sins "washed away" in baptism (Acts 22:16). Jesus has a glorious church by the members being "cleansed with the washing of water by the Word" (Ephesians 5:26). "Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water" (Hebrews 10:22).
The New Birth is therefore a begettal by the Spirit through the Word of God (Scriptures, 2 Timothy 3:16; 1 Corinthians 4:15; 1 Peter 1:22,25; Ephesians 6:17). The delivery of the new birth is being raised from the grave as a "new creature" (Romans 6:4; 2 Corinthians 5:17). A new babe in Christ (1 Peter 2:2).
Third, all that do the will of God delivered from Jesus through the apostles and prophets (Ephesians 2:20) have the assurance of salvation. "The wind bloweth where it listeth, and thou hearest the sound thereof, but canst not tell whence it cometh, and whither it goeth: so is every one that is born of the Spirit" (John 3:8). No one is perfect except Jesus (1 John 3:5). So a new born Christian may stumble at times (1 John 1:7-10) and admit it, but his life will exemplify a special spiritual conduct, a new life in which Christ dwells in one (Ephesians 3:17). "No one born of God makes a practice of sinning, for God's seed abides in him, and he cannot keep on sinning because he has been born of God" (1 John 3:9, English Standard Version 2011).
The application is simply this, how does your life measure up to the new birth, the birth of the Spirit which is required for your salvation?