And shall cast them into a furnace of fire: there shall be wailing and gnashing of teeth.

and these they will throw into the fiery furnace. There will be the weeping aloud and the gnashing of teeth.

And will put them into the fire; there will be weeping and cries of sorrow.

and will throw them into the blazing furnace, where there will be weeping and grinding of teeth.

And shall cast them into a furnace of fire. This is a metaphorical expression; for, as the infinite glory which is laid up for the sons of God so far exceeds all our senses, that we cannot find words to express it, so the punishment which awaits the reprobate is incomprehensible, and is therefore shadowed out according to the measure of our capacity. From ignorance of this, the Sophists have tortured themselves, to no purpose, by fruitless disputes, as we have already hinted on a former occasion. [1] Some commentators, I am aware, carry their ingenious inquiries into every minute phrase; but as there is reason to fear that subtleties, which rest on no solid grounds, may lead us into idle fooleries, I choose to philosophize more sparingly, and to rest satisfied with the plain and natural meaning. If we put a question to those who are so delighted with matters of curiosity, how it comes about that, while Christ is asleep, and unacquainted with the affair, the devil sows tares among the good seed, they will have nothing to reply; but while I desire to exercise caution, I have endeavored to leave out nothing that is useful and necessary to be known.

Footnotes

1 - Harmony, volume 1 [12]p. 200.

And shall cast them into a furnace of fire,.... Not a material, but a metaphorical one; denoting the wrath of God, which shall fall upon wicked men, and abide upon them to all eternity: which is sometimes called hell fire, sometimes a lake which burns with fire and brimstone; and here a furnace of fire, expressing the vehemency and intenseness of divine wrath, which will be intolerable; in allusion either to Nebuchadnezzar's fiery furnace, or as some think, to the custom of burning persons alive in some countries; or rather, to the burning of chaff and stubble, and the stalks of any unprofitable things that grew in the field (f), for the heating of furnaces, and is the very language of the Jews, who used to compare hell to a furnace; so Genesis 15:17 is paraphrased by them (g),
"And behold the sun set, and there was darkness; and lo! Abraham saw until the seats were set, and the thrones cast down; and lo! "hell", which is prepared for the wicked in the world to come, "as a furnace", which sparks and flames of fire surrounded; "in the midst of which", the wicked fell, because they rebelled against the law, in their lifetime.
Which is expressed in much the same language, and conveys the same ideas as here; and no wonder is it that it follows,
there shall be wailing and gnashing of teeth; declaring the remorse of conscience, the tortures of mind, the sense of inexpressible pain, and punishment, the wicked shall feel; also their furious rage and black despair,
(f) Misn. Sabbat. c. 3. sect. 1. & Maimon, & Bartenora in ib. (g) Hieros. Targum in Genesis. xv. 17.

And shall cast them into a furnace of fire--rather, "the furnace of fire":
there shall be wailing and gnashing of teeth--What terrific strength of language--the "casting" or "flinging" expressive of indignation, abhorrence, contempt (compare Psalm 9:17; Daniel 12:2): "the furnace of fire" denoting the fierceness of the torment: the "wailing" signifying the anguish this causes; while the "gnashing of teeth" is a graphic way of expressing the despair in which its remedilessness issues (see Matthew 8:12)!