To be born again is to become a Christian. Right? Yes. If so, then how can one be born again or how does one become a Christian?
Nicodemus, a good and religious man, a Pharisee and a ruler of the Jews, having been convinced that Jesus was sent from God into the world. came to Him by night. Nicodemus wanted to be part of Christ's kingdom and enjoy its blessings. Jesus, knowing this of Nicodemus, told him, "Except a man be born of water and of the spirit, he cannot enter into the kingdom of God." (John 3.5). Please read John 3.1-21. Nicodemus was part of the kingdom of Israel by being born into a Jewish family. He wanted to know how he could be part of Christ's kingdom which was being preached by John the Baptist and the apostles. Jesus' statement of "except a man be born again" is the only way one can enjoy the blessing and be part of the kingdom of God. In other words, to be a Christian and to be in the body of Christ one must be born again.
Jesus used physical birth to illustrate the spiritual birth. In this way the father begets and the mother brings forth the child, so the Holy Spirit begets and one is born again in baptism. "Of his own will begat he us with the word of truth, that we should be a kind of firstfruits of his creatures." (James 1.18). Read 1 Peter 1.22-23. The word of God is the sword of the spirit (Eph. 6.17). This word is what the Holy Spirit uses to produce faith in the human heart. When the word of God is preached, the Spirit by this means begets faith in the sinner's heart and that helps him to submit himself to be born again.
How is one born of the water? To be born of water is done by baptism which is a burial in water (Col. 2.12; Rom. 6.3-5). The purpose of baptism is for the remission of sins (Acts 2.38; 22.16). All those who were born again at and after Pentecost were requested to be baptized in order to be saved (Acts 22.16; 10.47-48; 2.36). By baptism the believer is put into the Lord's body (1 Cor. 12.13), which is the church (Col. 1.18,24). When one is put into Christ then he becomes a new creature (2 Cor. 5.17). When you become a new creature, then, you can say you are born again.
So it is necessary for all to be born again. And if one is born again, he is in the Kingdom of God which is the church of Christ. This new birth of water and the spirit occurs when the Holy Spirit begets faith through the word in the human heart and the believer responds by being baptized for the remission of sins.
In this we see that many who claim to be born again are not. You need to be born again but before then you must obey Christ - John 3.16, Mk. 16.15-16, 1 Cor. 15.1-4; Believe on Him - John 8.24, Heb. 11.6; Repent - Acts 2.38, Lk. 13.3-5; Confess Christ - Matt. 10.32, Rom. 10.9-10.