In the gospel of John, Jesus tells a teacher of the Jews named Nicodemus that he must be "born from above" to enter the kingdom of God. Throughout the New Testament, we continue to see the theme of "born of the spirit," "born again," "renewed," and "transformed" in the teachings of the apostles. To believe in Jesus and enter the kingdom of God, we need to be made into new creatures. We need to be re-born "from above" where Christ is so that we will be able to be with him.
Flesh Versus Spirit
Throughout Scripture, a contrast is made between what is of “the flesh” and what is of “the spirit.” By the flesh, the Bible does not mean our physical bodies, as opposed to our soul, but rather is referring to our state of corruption in sin. When we are first born, we are born into sin and destined for death (Ps. 51:5). What is natural to us is idolatry, self-righteousness, and sinful desires that lead to death. In order for us to enter God's kingdom, we must be made new so that what was natural (sin and death) no longer defines us (2 Cor. 5:17).
We need to be made into creatures not only worthy but able to be citizens in God's new heavens and new earth. This is why the Bible talks about our new selves as "born again" and “born of the spirit” (1 Pet. 1:3, 23; John 3:6). God's kingdom is a kingdom where death, sin, and corruption cannot enter. We need to be birthed by God himself (resurrected!) so that, once born of the Spirit, we no longer belong to the world but belong to the new creation. This new birth is accomplished by the inner work of the Holy Spirit when he renews and transforms our hearts and minds. By the power of the Holy Spirit we encounter Christ himself and are united to his death and resurrection. This is the initial stage of the resurrection promised us through Christ's own resurrection.
We Need a New Heart
Jesus' death and resurrection takes away the wrath of God and paid the price of sin so that we might have a living hope, Christ himself and eternal life. Without Christ, we are tied to a corrupt and sinful world with our hearts are turned away from God (Rom. 8:7). When the Holy Spirit gives us a new heart, he makes us no longer a part of this sinful world. Now, the Holy Spirit dwells in our hearts, giving us life and tying us to "above" where Christ, resurrected, waits for us (1 Pet. 1:3). With new hearts and minds we can now understand and believe the salvation given to us in Christ (1 Cor. 2:12).
Our participation in new life with Christ can only be worked in us by God himself through the Holy Spirit. This act of God is mysterious (Jn. 3:8). However, only by the power of God can a heart that is turned away from God and absorbed in sin be turned back towards him. Without the Holy Spirit dwelling in us giving us a new spirit of life, we will not and cannot have faith. By the Holy Spirit renewing us, however, we are made able and willing to receive God’s grace freely offered to us in Jesus Christ (2 Tim. 1:9–10).
Made for Another World
This act of God is a one-time, irreversible act. Once done, it cannot be undone: its effects are permanent. Once gained, you can never lose the inward work of the Holy Spirit. A new heart cannot return to its old ways, and a new spirit cannot return to evil. This is why John writes, "No one born of God makes a practice of sinning" (1 Jn. 3:9).
Then the angel showed me the river of the water of life, bright as crystal, flowing from the throne of God and of the Lamb through the middle of the street of the city; also, on either side of the river, the tree of life with its twelve kinds of fruit, yielding its fruit each month. The leaves of the tree were for the healing of the nations. No longer will there be anything accursed, but the throne of God and of the Lamb will be in it, and his servants will worship him. They will see his face, and his name will be on their foreheads. And night will be no more. They will need no light of lamp or sun, for the Lord God will be their light, and they will reign forever and ever. (Rev. 22:1-5)
While still incomplete on this earth, our final transformation will happen when we are glorified on the last day. Then we will be made into the very likeness of Christ, no longer able to be corrupted or able to sin but incorruptible and imperishable (1 Cor. 15:50-58; 1 Jn. 3:2-3). Then we will be fully fit for heaven (Rev. 21:3-4).