But a certain fearful looking for, etc. He means the torment of an evil conscience which the ungodly feel, who not only have no grace, but who also know that having tasted grace they have lost it forever through their own fault; such must not only be pricked and bitten, but also tormented and lacerated in a dreadful manner. Hence it is that they war rebelliously against God, for they cannot endure so strict a Judge. They indeed try in every way to remove the sense of God's wrath, but all in vain; for when God allows them a short respite, he soon draws them before his tribunal, and harasses them with the torments which they especially shun. He adds, fiery indignation, or the heat of fire; by which he means, as I think, a vehement impulse or a violent ardor. The word fire is a common metaphor; for as the ungodly are now in a heat through dread of divine wrath, so they shall then burn through the same feeling. Nor is it unknown to me, that the sophists have refinedly speculated as to this fire; but I have no regard of their glosses, since it is evident that it is the same mode of speaking as when Scripture connects fire with worm. (Isaiah 66:24.) But no man doubts but that worm is used metaphorically to designate that dreadful torment of conscience by which the ungodly are gnawed. [1] Which shall devour the adversaries. It shall so devour them as to destroy, but not to consume them; for it will be inextinguishable. And thus he reminds us, that they are all to be counted the enemies of Christ who have refused to hold the place granted them among the faithful; for there is no intermediate state, as they who depart from the Church give themselves up to Satan.

Footnotes

1 - It is puros zolos, "heat of fire;" which means hot or burning fire; the genitive here, as in some other instances, is the main subject. See [42]chapter 3:13, note. The language is still borrowed from the Old Testament: God often destroyed the rebellious among the Israelites with fire -- a symbol of the dreadful punishment of the wicked hereafter. See Leviticus 10:2; Numbers 16:35. The word zolos is properly heat, but is used in a variety of senses; heat of emulation -- "envy," Acts 13:45; -- of wrath -- "indignation" Acts 5:17; -- of concern, good and bad -- "zeal," Romans 10:2, and Philippians 3:6; -- of suspicion as to love -- "jealousy," 2-Corinthians 11:2; -- and of affection -- "love," 2-Corinthians 11:2. It is the context that determines the character of this heat. Here is has evidently its literal meaning, as being connected with fire, only the noun is used for the adjective. -- Ed

But a certain fearful looking for of judgment - The word "certain" here does not mean "fixed, sure, inevitable," as our translation would seem to imply. The Greek is the same as "a (τις tis) fearful expectation," etc. So it is rendered by Tyndale. The idea is, that if there was voluntary apostasy after having embraced the Christian religion, there could be nothing but an expectation of the judgment to come. There could be no other hope but that through the gospel, and as this would have been renounced, it would follow that the soul must perish. The "fearful apprehension" or expectation here does not refer so much to what would be in the mind itself, or what would be experienced, as to what must follow. It might be that the person referred to would have no realizing sense of all this, and still his situation be that of one who had nothing to expect but the terrors of the judgment to come.
And fiery indignation - Fire is often used in the Scriptures as an emblem of fierce punishment. The idea is, that the person referred to could expect nothing but the wrath of God.
Which shall devour the adversaries - All who become the adversaries or enemies of the Lord. Fire is often said to devour, or consume, and the meaning here is, that those who should thus become the enemies of the Lord must perish.

A certain fearful looking for of judgment - From this it is evident that God will pardon no man without a sacrifice for sin; for otherwise, as Dr. Macknight argues, it would not follow, from there remaining to apostates no more sacrifice for sin, that there must remain to them a dreadful expectation of judgment.
And fiery indignation - Και πυρος ζηλος· A zeal, or fervor of fire; something similar to the fire that came down from heaven and destroyed Korah and his company; Numbers 16:35.
Probably the apostle here refers to the case of the unbelieving Jews in general, as in chap. 6 to the dreadful judgment that was coming upon them, and the burning up their temple and city with fire. These people had, by the preaching of Christ and his apostles, received the knowledge of the truth. It was impossible that they could have witnessed his miracles and heard his doctrine without being convinced that he was the Messiah, and that their own system was at an end; but they rejected this only sacrifice at a time when God abolished their own: to that nation, therefore, there remained no other sacrifice for sin; therefore the dreadful judgment came, the fiery indignation was poured out, and they, as adversaries, were devoured by it.

But a certain fearful looking for of judgment and fiery indignation, which shall devour the (n) adversaries.
(n) For it is another matter to sin through the frailty of man's nature, and another thing to proclaim war on God as on an enemy.

But a certain fearful looking for of judgment,.... Either of some outward visible judgment in this life, which sometimes falls on such persons; or of the particular judgment which immediately follows after death; or of the universal judgment, after the resurrection, and the dreadful sentence of condemnation which will then pass, and be immediately executed; and which will be done by Christ, and according to truth, and in strict justice; it is certain, and there will be no escaping it, for it will be general. Now there is in this life an expectation in men of a future judgment, and in wicked men it is a fearful one; it is dreaded by them, and more especially in such men before described, when their consciences are awakened; it is a very dreadful one, inexpressibly so:
and fiery indignation, which shall devour the adversaries; which is to be understood, not of the fire of purgatory, for this is after judgment, that is pretended to be before it; this devours, that only purges, according to the Papists; this is for adversaries, that, as is supposed, is for friends: but perhaps some fiery judgment, expressive of the wrath and indignation of God, such as befell Sodom and Gomorrah, the two sons of Aaron, Nadab, and Abihu, and the men that rose up with Korah against Moses and Aaron: or rather the fire of hell, which is not corporeal and material, but is the wrath of God let down into the conscience; which shows the vile nature of sin, the strictness of God's justice, and the intolerableness of future punishment: and this is said to "devour the adversaries"; not only open ones, but secret, underhanded enemies, as the word here signifies; as such apostates are, before described, to God, and Christ, and the Spirit; to the Gospel, its doctrine, discipline, and ordinances; and to the children of God, and to the power of godliness in them: and with the fire of God's wrath they shall be devoured; not so as to be annihilated, but shall be eternally destroyed, both soul and body; that is, everlastingly punished, or punished with everlasting destruction.

a certain--an extraordinary and indescribable. The indefiniteness, as of something peculiar of its kind, makes the description the more terrible (compare Greek, James 1:18).
looking for--"expectation": a later sense of the Greek. ALFORD strangely translates, as the Greek usually means elsewhere, "reception." The transition is easy from "giving a reception to" something or someone, to "looking for." Contrast the "expecting" (the very same Greek as here), Hebrews 10:13, which refutes ALFORD.
fiery indignation--literally, "zeal of fire." Fire is personified: glow or ardor of fire, that is, of Him who is "a consuming fire."
devour--continually.