Palingenesis

Wiki:

Palingenesis is a concept of rebirth or re-creation, used in various contexts in philosophy, theology, politics, and biology. Its meaning stems from Greek palin, meaning 'again', and genesis, meaning 'birth'.

The word may be traced back to the Stoics,[2][3][4][5] who used the term for the continual re-creation of the universe. Similarly, Philo spoke of Noah and his sons as leaders of a renovation or rebirth of the earth, Plutarch of the transmigration of souls, and Cicero of his own return from exile.​

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It was a rather popular word used by Greek philosophers. It appears only 2 times in the NT in 2 different senses.

Berean Literal Bible, Matthew 19:

28 Jesus said to them, "Truly I say to you that in the regeneration,​

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παλινγενεσίας, palingenesias, Strong's 3824:

when the Son of Man shall sit down upon His throne of glory, you having followed Me, you also will sit on twelve thrones, judging the twelve tribes of Israel. 29 And everyone who has left houses, or brothers, or sisters, or father, or mother, or wife, or children, or lands, for the sake of My name, will receive a hundredfold, and will inherit eternal life.​

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I think Jesus was talking about the regeneration of the heavens and earth on the last day into the era of eternal life.

Elsewhere, Paul wrote in (ESV) Titus 3:

5 he saved us, not because of works done by us in righteousness, but according to his own mercy, by the washing of regeneration [G3824] and renewal of the Holy Spirit,

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renewal
ἀνακαινώσεως (anakainōseōs)
Strong's 342: Renewing; a renewal or change of heart and life. From anakainoo; renovation.

I think Paul was talking about the regeneration of the human spirit, i.e., being born again.

In the NT, palingenesis (G342) can mean the regeneration of a person now or the regeneration of the universe in the future.

I define salvation as a 3-stages process:

1. Regeneration: Paraclete indwells the human spirit instantly and presently.
2. Sanctification of the soul involves ongoing faithful works daily.
3. Glorification of bodies at the resurrection on the last day. Regeneration of the universe.

Palingenesis refers to the first or the last stage.