Jesus said plainly, “Most assuredly, I say to you, unless one is born again, he cannot see the kingdom of God” (John 3:3). Again He said, “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” (John 3:5–6). This shows why man must be born again. We are born once in flesh, but that flesh is weak and cannot inherit the kingdom of God. We need a new life from the Spirit, to be made alive in God.
When the Sadducees questioned about the resurrection, Jesus answered, “For when they rise from the dead, they neither marry nor are given in marriage, but are like angels in heaven. But concerning the dead, that they rise, have you not read in the book of Moses… ‘I am the God of Abraham, the God of Isaac, and the God of Jacob’? He is not the God of the dead, but the God of the living” (Mark 12:25–27). Here Jesus teaches that Abraham, Isaac, and Jacob are alive to God. Though their bodies died, their spirits live, waiting for the resurrection.
Jesus Himself is the first to rise from the dead never to die again. He said, “I am the resurrection and the life. He who believes in Me, though he may die, he shall live. And whoever lives and believes in Me shall never die” (John 11:25–26). This is why those who belong to Him must be born again. They pass from death to life even now in spirit, and in the last day He will raise them up in a body that cannot die (John 6:40, 54). The disciples also speak the same way. Peter declared, “Blessed be the God and Father of our Lord Jesus Christ, who according to His abundant mercy has begotten us again to a living hope through the resurrection of Jesus Christ from the dead” (1 Peter 1:3). Being “begotten again” is the new birth, tied directly to the resurrection of Christ.
Paul speaks in agreement with this, saying, “And you He made alive, who were dead in trespasses and sins” (Ephesians 2:1). He explains further, “Even when we were dead in trespasses, [God] made us alive together with Christ…and raised us up together, and made us sit together in the heavenly places in Christ Jesus” (Ephesians 2:4–6). This means believers are already raised spiritually with Christ, though we wait still for the body to be raised immortal and incorruptible.
When Christ rose and ascended, “He led captivity captive” (Ephesians 4:8). This points to the faithful of old being taken up with Him, no longer held in death, but alive to God through His victory. That is why Jesus said God is not God of the dead, but of the living.
So we see: mankind must be born again because the kingdom of God is not for flesh and blood as we are now, but for those made alive by the Spirit. Christ came, died, and rose again so that both the saints before Him and those after might be alive to God. Those who believe are already alive in spirit, and on the last day they will be raised in a body that cannot die, to live with Him forever on the new earth.