In his book The Fire That Consumes Fudge devotes an entire chapter (chapter 4) to the meaning of the Greek word aiōnios (usually translated ‘eternal’).
The key question is this: does the word mean (a) everlasting, (b) characteristic of the age to come, or (c) either or both of these (depending on context)?
A key text is Matthew 25:46, which speaks both of ‘eternal life’ and ‘eternal punishment’. Many argue that aiōnios must mean the same in both parts of the verse. If eternal life is endless, so also must eternal punishment be.
Shedd insists: ‘The truth is, that aiōn is a term that denotes time only, and never denotes the nature and quality of an object.’
On the other hand, F. W. Farrar maintained with equal certainty that there was ‘no authority whatever for rendering it “everlasting”‘.
According to Fudge:-
‘Petavel points out that Scripture frequently uses aiōn, aiōnios and their Hebrew counterparts (olam in various forms) of things that have come to an end. The sprinkling of blood at the Passover was an “everlasting” ordinance (Exod 12:24). So were the Aaronic priesthood (Exod 29:9; 40:15; Lev 3:17), Caleb’s inheritance (Josh 14:9), Solomon’s temple (1 Kgs 8:12–13), the period of a slave’s life (Deut 15:17), Gehazi’s leprosy (2 Kgs 5:27)—and practically every other ordinance, rite, or institution of the Old Testament system. These things did not last “forever” in the sense of “time extended without limitation.” They did last beyond the vision of those who first heard them called “everlasting,” and no time limit was then set at all.’
In common with Jewish thought, the NT writers divide time into two overlapping ‘ages’ – the present age, and the age to come (Matt 12:32; Luke 20:34–35). When Jesus and the apostles speak and write of the present age, it is clear that they are not thinking merely of a span of time, but of certain characteristics:-
As Fudge states:
Jesus speaks of the cares of this age (Matt 13:22; Mark 4:19), the sons of this age (Luke 16:8) and the end of this age (Matt 13:39–40; 24:3; 28:20). Paul also speaks of this age with its debaters (1 Cor 1:20), wisdom and rulers (1 Cor 2:6, 8; 3:18), course of life (Eph 2:2), world rulers (Eph 6:12 KJV), and the rich (1 Tim 6:17). Over against this age he also contrasts the age to come (Eph 1:21).
The present age is under Satan’s dominion (2 Cor 4:4), and Christ gave himself for our sins to rescue us from it (Gal 1:4). The age to come is of another order that may be called “eternal.” To be guilty of an “eternal” sin (Mark 3:29) is to be guilty of one that will not be forgiven even in the age to come (Matt 12:32).
Whereas John’s Gospel speaks often of ‘eternal life’, the Synoptics refer to ‘the kingdom of God’, further confirming a qualitative meaning for the former expression. In fact, the two are sometimes used interchangeably (Matt 19:16–17, 23; Mark 9:45, 47; cf. John 3:3, 5, 15, 16). To inherit the kingdom is to enter into eternal life (Matt 25:34, 46).
Scripture makes it clear that the bliss of the righteous is everlasting, even if aiōnios had only a qualitative meaning, and no quantitative meaning:-
Nothing can ever separate God’s people from his love—even things to come (Rom 8:38–39). They will “always” be with the Lord (pantote, literally “every-then,” 1 Thess 4:17). God will glorify them and give them a body that cannot die (1 Cor 15:53–54).
There are five passages in which the adjective aiōnios modifies a noun that indicates the result of an action. There are: eternal salvation (Heb 5:9), eternal redemption (Heb 9:12), eternal judgment (Heb 6:2), eternal punishment (Matt 25:46), and eternal destruction (2 Thess 1:9). In each case (maintains Fudge) we should understand that something has taken place in time that has everlasting consequence.
Fudge concludes that it is mistaken to ascribe to aiōnios either an exclusively qualitative or an exclusively quantitative meaning.
[See also this review of Ilaria Ramelli and David Konstan, Terms for Eternity: Aiônios and Aïdios in Classical and Christian Texts (Gorgias Press, 2013)]