who will be born during the Millennial Reign of Jesus Christ
might live much longer than Methuselah?
Ponder this…
Background
When Adam sinned, he effectively delegated to satan full authority that God had previously delegated to mankind. Thus, satan literally became the god in and of this world and all its systems, visible and invisible. This authority included 'spiritual ownership' of every person who, directly and indirectly, would ever be conceived from Adam’s seed. This spiritual ownership is akin to slavery, and The Bible reveals all humans are born as slaves to sin. satan is the king of sinfulness, as it originated with him when he led a rebellion in Heaven against Jesus, The Lord God.
God’s 'multi-millennial, strategic plan' for humans is to extend to all humans His Grace of salvation in Jesus Christ. This includes (1) people who were/will be conceived, but who were never born; (2) people who were/will be born, but who never reach(ed) God’s ‘age of accountability’; and (3) people who will have matured to, and beyond His age of accountability. To implement God’s plan, Jesus came, died sacrificially, and was resurrected to break the power of this slavery, and to create a new race of redeemed humans who were once slaves. (And yes, satan even owned the fetuses, people who were conceived and aborted.) *
The Bible indicates only a relatively small remnant of humanity will actually elect to benefit from God’s offer of salvation and eternal life in Christ. I understand and believe that, by His Grace, people who are conceived, but who are never born, or who never reach His age of accountability, will be included in this remnant group. (Imagine children of non-Christian parents in Heaven.) But people who reach His age of accountability, and who, by faith, embrace His plan of salvation, will have been both owned, tempted and deceived by satan to reject all things Godly, but by faith, they will have demonstratively proven they embraced God's offer of salvation in Christ. This is what I understand is the foundation of ‘Christian salvation and spiritual rebirth in Christ’. The New Testament exposits what and how they/we are to build upon this foundation, in terms of personal and corporate standards of comportment and conduct.
Millennium
During the Millennial Reign, Jesus will temporarily be God in and of this world and all its systems. satan and presumably all his rank files of devils and demons will be locked away for 1,000 years, unable to own anyone who is born during the Millennial Reign, or to tempt and deceive any human being, irrespective of when he/she will have been born. (Revelation 20) The first generation in this period (age) will be folks who will have been born before the Millennial Reign. They will be survivors (remnants) from the pre-millennial time. (See: The Worst of the Worst (Poem)) They will have willingly received the anti-Christ’s mark of the beast, akin to a physical branding or perhaps a permanent tattoo, that will have allowed them to engage commercially during the great tribulation plagues. (See: Mark of the Beast (Q&A)) Thus, though satan and his cohorts will 'not be on the scene', these people will have been, and will still be spiritually owned by him; they will have forever rejected God's offer of salvation in Jesus Christ; and they will not be allowed that choice again, per Revelation 14:10-11. Some will have attempted suicide during the tribulation plagues, but will have been denied death, per Revelation 9:6. Yet as physical/mortal human beings, they will indeed eventually die. So what will be their main purpose in the Millennial Reign?
Ahhhhh… before they die, just like Adam and Eve, and Noah’ family, they will sire and raise a new generation of human beings (‘millennials’) to re-populate Earth during the Millennial Reign! NB: The Lord reiterates this pattern in the transitions between the first-to-second (pre-flood-to-post-flood) age, and the fourth-to-fifth (tribulation-to-Millennial Reign) age of human existence. See: The Anti-Christ (Series), especially Part 5.
But what of these millennials? Will some of them possibly be saved? This question has spawned many interpretations and understandings of prophetic Scripture. Reviewing some of them reveals a considerable gap that must be addressed…
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* In Psalm 51:5, David confirms he was conceived in iniquity, testifying to his (and our) sinful nature. The age of accountability is believed to be the age at which a child is spiritually accountable to understand good from evil, and therefore be responsible for his/her words and actions. See: What is the age of accountability?