And he shall set the sheep on his right hand, but the goats on the left. And then will I profess unto them, I never knew you: depart from me, ye that work iniquity. Depart from me, all ye workers of iniquity; for the LORD hath heard the voice of my weeping.
~ Matthew 25:33, Matthew 7:23, Psalm 6:8

Thou hast rebuked the proud that are cursed, which do err from thy commandments. And these shall go away into everlasting punishment: but the righteous into life eternal. What if God, willing to shew his wrath, and to make his power known, endured with much longsuffering the vessels of wrath fitted to destruction: And that he might make known the riches of his glory on the vessels of mercy, which he had afore prepared unto glory, And the angels which kept not their first estate, but left their own habitation, he hath reserved in everlasting chains under darkness unto the judgment of the great day.
~ Psalm 119:21, Matthew 25:46, Romans 9:22-23, Jude 1:6

The Torments of Loss, by Thomas Boston. The following is an excerpt from his work, “Of Hell”.

Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:
~ Matthew 25:41

The punishment of loss that the damned shall undergo is separation from the Lord. We learn (this) from the text…They shall be eternally separated from God and Christ. Christ is the way to the Father; but the way to them shall be everlastingly blocked up, the bridge shall be drawn, and the great gulf fixed. (Then) shall they be shut up in a state of eternal separation from God the Father, Son, and Holy Ghost. They will be locally separated from the Man Christ and shall never come into the seat of the blessed, where He appears in His glory. (They will) be cast out into outer darkness (Mat 22:13). They cannot indeed be locally separated from God, (for) they cannot be in a place where He is not. He is and will be present everywhere: “If I make my bed in hell,” says the Psalmist, “behold thou art there” (Psa 139:8). But they shall be miserable beyond expression in a relative separation from God. Though He will be present in the very centre of their souls, if I may so express it, while they are wrapped up in fiery flames in outer darkness, it shall only be to feed them with…His wrath and to punish them with the emanations of His revenging justice. They shall never more taste of His goodness and bounty nor have the least glimpse of hope from Him. They will see His heart to be absolutely alienated from them and that it cannot be towards them. (They will see) that they are the party against whom the Lord will have indignation forever. They shall be deprived of the glorious presence and enjoyment of God. They shall have no part in the beatific vision nor see anything in God towards them, but one wave of wrath rolling after another. This will bring upon them overwhelming floods of sorrow forevermore. They shall never taste of the rivers of pleasures that the saints in heaven enjoy, but shall have an everlasting winter and a perpetual night because the Sun of righteousness has departed from them. They are left in outer darkness. So great as heaven’s happiness is, so great will be their loss. They can have none of it forever.

This separation of the wicked from God will be 1. An involuntary separation. Now they depart from Him; they will not come to Him, though they are called and entreated to come. Then they shall be driven away from Him, when they would gladly abide with Him…2. It will be a total and utter separation…There shall be a total separation, the damned being cast into utter darkness, where there will not be the least gleam of light and favour from the Lord…3. It shall be a final separation. They will part with Him…being shut up under everlasting horror and despair…Never shall one message of favour or goodwill go between (Jesus Christ and them) anymore.

This punishment of loss in a total and final separation from God is a misery beyond what mortals can conceive and which only the dreadful experience of the damned can sufficiently unfold. But that we may have some conception of the horror of it, let these following things be considered:

(1) God is the chief good. Therefore, to be separated from Him must be the chief evil…God being the chief good and no good comparable to Him, there can be no loss as great as the loss of God. The full enjoyment of Him is the highest pinnacle of happiness the creature is capable of arriving at. To be separated fully and finally from Him must then be the lowest step of misery that the rational creature can be reduced to…What must it then be to be rejected of God, of goodness itself?

(2) God is the fountain of all goodness. From (Him), all goodness flows unto the creatures and…is continued in them and to them. Whatever goodness or perfection, natural as well as moral, is in any creature, it is from God…Wherefore, a total separation from God, wherein all comfortable communication between God and a rational creature is absolutely blocked up must of necessity bring along with it a total eclipse of all light of comfort and ease whatsoever…Our Lord tells us, “There is none good but one, that is, God” (Mat 19:17). Nothing good or comfortable is originally from the creature. Whatever good or comfortable thing one finds in one’s self, as health of body (or) peace of mind; whatever sweetness, rest, pleasure, or delight one finds in other creatures, as in meat, drink, arts, and sciences—all these are but some faint rays of Divine perfections, communicated from God unto the creature. (These depend) on a constant influence from Him for their conservation, which failing, they would immediately be gone. For it is impossible that any created thing can be to us more or better than what God makes it to be. All the rivulets of comfort we drink, within or without ourselves, come from God as their springhead…Thus, in their separation from God, all peace is removed far away from them, and pain in body and anguish of soul succeed to it. All joy goes, and unmixed sorrow settles in them. All quiet and rest separate from them, and they are filled with horror and rage. Hope flies away, and despair seizes them. Common operations of the Spirit, which now restrain them, are withdrawn forever, and sin comes to its utmost height. Thus, we have a dismal view of the horrible spectacle of sin and misery, which a creature proves when totally separated from God and left to itself. We may see this separation to be the very hell of hell.

Being separated from God, they are deprived of all good. The good things that they set their hearts upon in this world are beyond their reach there. The covetous man cannot enjoy his wealth there, the ambitious man his honours, nor the sensual man his pleasures—no, not a drop of water to cool his tongue (Luk 16:24-25). No meat or drink there to strengthen the faint; no sleep to refresh the weary; no music or pleasant company to comfort and cheer up the sorrowful. As for those good things they despised in the world, they shall never more hear of them nor see them. No (calls to) Christ there—no pardon, no peace, no wells of salvation in the pit of destruction. In one word, they shall be deprived of whatever might comfort them, being totally and finally separated from God, the Fountain of all goodness and comfort.

(3) Man naturally desires to be happy. Being conscious…that he is not self-sufficient, he has ever a desire of something (outside) himself to make him happy. The soul being by its natural make and constitution capable of enjoying God and nothing else being (proportional) to its desires, it can never have true and solid rest until it rests in the enjoyment of God. The rational nature can never lay aside this desire of happiness, no, not in hell. Now, while the wicked are on earth, they seek their satisfaction in (created things). When one fails, they go to another. Thus they spend their time in the world, deceiving their own souls with vain hopes. But in the other world, all comfort in the creatures failing and the shadows that they are now pursuing vanished in a moment, they shall be totally and finally separated from God and see they have thus lost Him…This will create unspeakable anguish: they shall live under an eternal, gnawing hunger after happiness that they certainly know shall never be in the least measure satisfied, all doors being closed on them. Who then can imagine how this separation from God shall cut the damned to the heart? How they will roar and rage under it? How it will sting and gnaw them through the ages of eternity?

(4) The damned shall know that some are perfectly happy in the enjoyment of that God from Whom they themselves are separated. This will aggravate the sense of their loss: they can never have any share with those happy ones. Being separated from God, they are separated from the society of the glorified saints and angels…We have ground from the Word to conclude that the damned shall have a very exquisite knowledge of the happiness of the saints in heaven. What else can be meant of the rich man in hell seeing Lazarus in Abraham’s bosom? One thing is plain: in this case, their own torments will give them such notions of the happiness of the saints as a sick man has of health or a prisoner has of liberty. And as they cannot fail of reflecting on the happiness of those in heaven without any hope of attaining to contentment with their own lot, so every thought of that happiness will aggravate their loss…

(5) They will remember that time was when they might have been made partakers of the blessed company of saints in their enjoyment of God. This will aggravate their sense of the loss…Despisers of the Gospel will remember with bitterness that Jesus Christ with all His benefits was (preached) to them; that they were exhorted, entreated, and pressed to (believe), but would not; and that they were warned of the misery they feel and exhorted to flee from the wrath to come—but they would not hearken. The Gospel…slighted will make a hot hell…

(6) They will see the loss to be irrecoverable: that they must eternally lie under it, never, never to be repaired. Might the damned, after millions of ages in hell, regain what they have lost, it would be some ground of hope. But the prize is gone and can never be recovered. Two things will pierce them to the heart: 1. that they never knew the worth of it until it was irrecoverably lost…2. that they have lost it for dross and dung…They have lost heaven for earthly profits and pleasures, and now both are gone together from them. The drunkard’s cups are gone, the covetous man’s gain, the voluptuous man’s carnal delights, and the sluggard’s ease: nothing is left to comfort them now. The happiness they lost remains indeed, but they can have no part in it forever.