The classic passage from the Bible that answers this question is John 3:1-21. The Lord Jesus the Christ is talking to Nicodemus, a prominent Pharisee and member of the Sanhedrin (the ruling body of the Jews). Nicodemus had come to Jesus at night with some questions.
As Jesus talked with Nicodemus, “Jesus answered and said unto him, Verily, verily, I say unto thee, Except a man be born again, he cannot see the kingdom of God. Nicodemus saith unto him, How can a man be born when he is old? can he enter the second time into his mother's womb, and be born? Jesus answered, Verily, verily, I say unto thee, Except a man be born of water and of the Spirit, he cannot enter into the kingdom of God. That which is born of the flesh is flesh; and that which is born of the Spirit is spirit. Marvel not that I said unto thee, Ye must be born again.” John 3:3-7
The phrase "born again" literally means "born from above." Nicodemus had a real need. He needed a change of his heart—a spiritual transformation. New birth, being born again, is an act of God whereby eternal life is imparted to the person who believes (2 Corinthians 5:17; Titus 3:5; 1 Peter 1:3; 1 John 2:29; 3:9; 4:7; 5:1-4, 18). John 1:12, 13 indicates that being "born again" also carries the idea of "becoming children of God" through trust in the name of Jesus the Christ.
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