Regeneration, or the new birth, is a supernatural, monergistic work of God the Holy Spirit by which He gives spiritual life to those who are dead in sin, making them partakers of a new nature. It is the necessary first step of salvation, preceding and enabling true repentance and faith in Jesus Christ.
Regeneration is not a result of human effort, moral improvement, or religious ritual; it is a creative act of God. Just as a physical corpse cannot raise itself to life, those who are spiritually dead in trespasses and sins cannot contribute to their own quickening. As taught in the Canons of Dort Head 3 Article 12, this is a 'supernatural work' which God performs without our aid. It is often likened by our Lord to the wind, which moves sovereignly and according to God's own will—we see its effects, but the secret operation remains a divine mystery (John 3:3-8).
The primary effect of regeneration is the transformation of the heart. The prophet Ezekiel speaks of God taking away the 'stony heart' of rebellion and replacing it with a 'heart of flesh' that is responsive to His Word (Ezekiel 36:26). This is not merely an external reformation, but an internal change of nature. As we are told in the Heidelberg Catechism Question 8, we are wholly incapable of doing any good, being inclined to all wickedness, unless we are regenerated by the Spirit of God. This new birth creates a new person in Christ, where the desires, will, and affections are fundamentally reoriented toward God.
Regeneration is the foundation of our entire standing before God. Because we were 'dead in trespasses and sins,' God, being rich in mercy, made us alive together with Christ (Ephesians 2:1, 4-7). This life-giving grace brings us to see our need for a Savior, leading us to faith and repentance. We do not act in order to be born again; rather, because we have been born again by the sovereign grace of God, we are enabled to believe. All of this points to the glory of the gospel: we are accepted and loved in Christ, and it is His work—from beginning to end—that secures our salvation.