Summary: True Christians receive the down payment or the promise of eternal life when God begets them with the Holy Spirit. (Ephesians 1:14.) The church’s immortal eternal life is realized in the resurrection. In the world’s resurrection during Christ’s earthly kingdom, the willing of mankind will learn to embrace God’s law of love. Their loyalty will be tested. Those faithful will rejoice with eternal human life, but they will still be mortal.
Discussion: All of mankind are children of Adam and all are under the penalty of death. Romans 5:12, 18 (NKJV), “…through one man sin entered the world, and death through sin, and thus death spread to all men,…”
Eternal life is a gift. (Romans 6:23) This gift is received in the resurrection. John 6:47, 51, 54 (ESV), “Truly, truly, I say to you, whoever believes has eternal life … Whoever feeds on my flesh and drinks my blood has eternal life, and I will raise him up on the last day.”
In the resurrection, the being (or soul) may be resurrected with a spirit body or a natural human body. The Apostle Paul wrote, “…what you sow (your character) is not made alive unless it dies. And what you sow, you do not sow that body that shall be, but mere grain–perhaps wheat (true, faithful Christians) or some other grain. But God gives it (the being) a body as He pleases, and to each seed its own body… There are also celestial (heavenly, spirit) bodies and terrestrial (earthly) bodies; but the glory of the celestial is one, and the glory of the terrestrial is another.” – 1 Corinthians 15:36-38, 40 (NKJV)
The immortal or death-proof spirit body will be given to the Bride of Christ. This body will have eternal life within itself. (John 7:38) Whereas, mortal (existence depending on air, water, food, etc.) eternal life will be granted to those of mankind who will learn to embrace God’s Law of Love during Christ’s reign on Earth. Jesus explained this Law in Luke 10:27 (NKJV), “… ‘You shall love the LORD your God with all your heart, with all your soul, with all your strength, and with all your mind,’ and ‘your neighbor as yourself.’”
Thus, eternal life or life without end will be granted in the resurrection to those who love God supremely. For the church, the nature of the life will be spiritual and no longer capable of dying. For the earthly, the life will continue forever, but they will be mortal.
During Christ’s 1,000 year reign, mankind will need to develop a Christ-like character and prove their loyalty to God to maintain their gift of eternal life. But the Church class will receive the great reward of immortality (Romans 2:7, Revelation 2:10), because they were developed and proved faithful through the trials of this present evil world (Galatians 1:4).