We need to quickly run through several of the verses speaking in terms of things “eternal” or aionios. The point is to demonstrate that aionios refers to the next age but not necessarily to everlasting.
(Mark 3:29) But whoever blasphemes against the Holy Spirit will never be forgiven; he is guilty of an eternal sin.”
Now, Jesus plainly isn’t saying that this sin is an everlasting sin. Rather, the consequences of the sin will be everlasting. The sin will be with us even into the next age, where it will truly matter.
(Mark 10:29-30) “I tell you the truth,” Jesus replied, “no one who has left home or brothers or sisters or mother or father or children or fields for me and the gospel 30 will fail to receive a hundred times as much in this present age (homes, brothers, sisters, mothers, children and fields — and with them, persecutions) and in the age to come, eternal life.
Now, by now the meaning will be clear. “Eternal life” will last forever, but it’s eternal because it’s life in the next age. Jesus’ contrast is plainly this-age vs. next-age.
(John 5:24) “I tell you the truth, whoever hears my word and believes him who sent me has eternal life and will not be condemned; he has crossed over from death to life.
(John 6:47-50) I tell you the truth, he who believes has everlasting life. 48 I am the bread of life. 49 Your forefathers ate the manna in the desert, yet they died. 50 But here is the bread that comes down from heaven, which a man may eat and not die.
(Rom 6:23) For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
(Gal 6:8) The one who sows to please his sinful nature, from that nature will reap destruction; the one who sows to please the Spirit, from the Spirit will reap eternal life.
Over and over, we’re told that the choice is between life and death, obviously enough not in this age, but in the next. In eternity, we’ll either be destroyed and die or else be rescued and live. For ever and ever.
When a writer wants to say “everlasting” he has another word available: aidios, meaning lasting forever, either forward in time or both backwards and forwards. The New Testament writers use it twice —
(Rom 1:20) For since the creation of the world God’s invisible qualities–his eternal power and divine nature — have been clearly seen, being understood from what has been made, so that men are without excuse.
(Jude 1:6) And the angels who did not keep their positions of authority but abandoned their own home — these he has kept in darkness, bound with everlasting chains for judgment on the great Day.
While Paul uses the word according to its classic definition in Romans, Jude refers to everlasting chains but chains that will only be needed until Judgment Day — which I don’t really understand. Perhaps the assumption is that the chains will be needed afterwards, too. After all, the fate of the angels who rebelled against God is not going to be a pleasant one.