Question: "What is regeneration according to the Bible?"
Answer: Another word for regeneration is rebirth, from which we get the phrase “born again.” To be born again is opposed to, and distinguished from, our first birth, when we were conceived in sin. The new birth is a spiritual, holy, and heavenly birth signified by a being made alive in a spiritual sense. Our first birth, on the other hand, was one of spiritual death because of inherited sin. Man in his natural state is “dead in trespasses and sins” until we are “made alive” (regenerated) by Christ when we place our faith in Him (Ephesians 2:1). After regeneration, we begin to see, and hear, and seek after divine things, and to live a life of faith and holiness. Now Christ is formed in the hearts; we are now partakers of the divine nature, having been made new creatures. God, not man, is the source of this (Ephesians 2:1, 8). It is not by men's works, but by God’s own good will and pleasure. His great love and free gift, His rich grace and abundant mercy, are the cause of it and these attributes of God are displayed in the regeneration and conversion of sinners.
Regeneration is part of the "salvation package," if you will, along with sealing (Ephesians 1:14), adoption (Galatians 4:5), reconciliation (2 Corinthians 5:18-20), and many other salvation concepts. Being born again or born from above is parallel to regeneration (John 3:6-7; Ephesians 2:1; 1 Peter 1:23; John 1:13; 1 John 3:9; 4:7; 5:1, 4, 18). Simply put, regeneration is God making a person spiritually alive, a new creation, as a result of faith in Jesus Christ. The reason regeneration is necessary is that prior to salvation we are not God's children (John 1:12-13); rather, we are children of wrath (Ephesians 2:3; Romans 5:18-20). Before salvation, we are degenerate. After salvation we are regenerated. The result of regeneration is peace with God (Romans 5:1), new life (Titus 3:5; 2 Corinthians 5:17), and eternal sonship (John 1:12-13; Galatians 3:26). This regeneration is eternal and begins the process of sanctification wherein we become the people God intended for us to be (Romans 8:28-30).
The Bible is clear that the only means of regeneration is by faith in the finished work of Christ on the cross. No amount of good works or keeping of the law can regenerate the heart which from birth is “deceitful and wicked above all things” (Jeremiah 17:9). This concept of the new birth is unique to Christianity. No other religion offers a cure for the total depravity of the human heart, preferring instead to outline an often massive body of works and deeds that must be done to gain favor with God. God has told us, though, that “by works of the law no human being will be justified in his sight” (Romans 3:20). Total regeneration of the heart is necessary for salvation. Paul explains this concept perfectly in Galatians 2:20: “I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. And the life I now live in the flesh I live by faith in the Son of God, who loved me and gave himself for me.” This is true regeneration.