Charles Ellicott Commentary Matthew 25:46

"And these shall go away into eternal punishment: but the righteous into eternal life." — Matthew 25:46 (ASV)

Everlasting punishment ... life eternal — The two adjectives, "everlasting" and "eternal," represent the same Greek word, αἰώνιος. Therefore, the same English word should have been used in both clauses. Of the two, "eternal" is linguistically preferable. It is traceably connected to the Greek, as the Latin aeternus is derived from aetas, which comes from aevum—another form of the Greek αἰών (aion). The passage's bearing on the nature and duration of future punishment is too important to overlook. While this question is too broad to be settled by a single text, everything this verse contributes to the discussion must be fully and fairly weighed.

On the one hand, it is argued that since we understand "eternal life" to have no end, we must also accept the endlessness of the "eternal fire."

On the other hand, it must be admitted that:

1. The Greek word translated "eternal" does not in itself mean "endless" but rather refers to a long duration, whether for a single age or a succession of ages. It is therefore applied in the New Testament to periods of time that have both a beginning and an end (Romans 16:25, where the Greek means "from aionian times," translated as since the world began; compare to 2 Timothy 1:9 and Titus 1:2). It is also used in the Greek Old Testament for institutions and ordinances that were acknowledged to grow old and pass away (Genesis 17:8; Leviticus 3:17).
2. In the writings of a Greek Father, Gregory of Nyssa (who held to the doctrine of the restitution of all things), the word is even connected with "interval." He used it to express the duration of a disciplinary punishment that he believed would end after an aionian intervening period.

Strictly speaking, then, the word itself—apart from any qualifying noun—implies a vast, undefined duration rather than endlessness in the full sense of the word "infinite."

The solemnity of these words, coming at the close of the great prophecy of judgment, clearly suggests that our Lord intended His disciples—and through them, His people in all ages—to reflect on the finality of the division that judgment entails. People will reap what they have sown. The consequences of evil deeds, or of the failure to do good, must naturally result in a retribution that, as far as we can see, has no definable end.

However, there are further considerations:

1. The symbolism in Scripture suggests that "fire" is not necessarily a material element inflicting unbearable physical torture. Instead, the penalty for sin may be an intense and terrible awareness of the presence of God—who is a consuming fire (Hebrews 12:29) in His infinite holiness—combined with the sense of being opposed to Him and therefore under condemnation.
2. Even assuming the punishment is perpetual, this does not necessarily mean that all the condemned suffer equally at any given time, or that any single soul's suffering remains constant throughout its duration. While not overemphasizing the point, the Greek word for "punishment" used here was understood by ethical writers like Aristotle to mean reformative, rather than purely vindictive or retributive, suffering (Aristot. Rhet. i. 10). It is conceivable that accepting suffering as deserved could lessen its severity. Furthermore, we cannot, consistent with a true understanding of God, imagine Him fixing any created will into an attitude of permanent resistance by an irresistible decree. That such resistance is tragically possible is clear from wide and painful experience. Since the "hardening" in such cases results from a divine law, it can, from one perspective, be described as God's act (Romans 9:18). Yet, experience also shows that while suffering remains suffering, it can lose some of its bitterness when accepted as deserved. The law of continuity and analogy, which must be given some weight in our thoughts about the life to come, suggests this may also be true in the hereafter. (For other aspects of this momentous question, see the notes on Matthew 5:26 and Matthew 18:34).
3. Regarding the nature of the "eternal life" promised to those who follow the Light that enlightens everyone, we must remember our Lord's own definition. Within a few hours of speaking these words, He said, This is life eternal, that they might know Thee the only true God, and Jesus Christ whom Thou hast sent (John 17:3).

By its very nature, this life tends toward perpetuity. It is absolutely inconceivable that it should fail and cease after lasting through the ages implied by the word "eternal," regardless of its precise etymological explanation.