From gotquestions.org
Question: "What does it mean to be a born again Christian?"
Answer: What does it mean to be a born again Christian? The classic passage from the Bible that answers this question is John 3:1-21. The Lord Jesus Christ is talking to Nicodemus, a prominent Pharisee and member of the Sanhedrin (a ruler of the Jews). Nicodemus had come to Jesus at night. Nicodemus had questions to ask Jesus.
As Jesus talked with Nicodemus, He said "...Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God." Nicodemus said to Him, "How can a man be born when he is old? Can he enter a second time into his mother's womb and be born?" Jesus answered, "Most assuredly, I say to you, unless one is born of water and the Spirit, he cannot enter the kingdom of God. That which is born of the flesh is flesh, and that which is born of the Spirit is spirit. Do not marvel that I said to you, You 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 "born again" also carries the idea "to become children of God" through trust in the name of Jesus Christ.
The question logically comes, "Why does a person need to be born again?" The Apostle Paul in Ephesians 2:1 says, "And you He made alive, who were dead in trespasses and sins..." To the Romans in Romans 3:23, the Apostle wrote, "For all have sinned and come short of the glory of God." So, a person needs to be born again in order to have their sins forgiven and have a relationship with God.
How does that come to be? Ephesians 2:8,9 states, "For by grace you have been saved through faith, and that not of yourselves; it is the gift of God, not of works lest any man should boast." When one is "saved," he/she has been born again, spiritually renewed, and is now a child of God by right of new birth. Trusting in Jesus Christ, the One who paid the penalty of sin when He died on the cross, is what it means to be "born again" spiritually. "Therefore, if any man be in Christ, he is a new creation..." (2 Corinthians 5:17a).
"But as many as received Him, to them He gave the right to become children of God, to those who believe on His name: who were born, not of blood, nor of the will of the flesh, nor of the will of man, but of God" (John 1:12-13).