Question

Is hell eternal? If so, then did a certain number of men and women walking the earth leave hell (Mark 3:29, Matt. 18:18)?

Answer

Matthew 18:18 is referring to the assurance of the forgiveness of sins, which Jesus offers to those who repent and believe. His disciples were commissioned to grant such assurance in His Name, but also to warn the unrepentant of the certainty of their demise. Mark 3:29 likewise warns against remaining unrepentant in the face of the Holy Spirit’s testimony concerning Christ and forgiveness. To so blaspheme the Spirit can only bring eternal death. I do not believe either passage speaks of people leaving hell to walk the earth. One Hebrew word and three Greek words are found in the Scriptures and rendered as “hell” in English translations: Sheol (pit, grave), referring to the unseen world where the dead languish or the unborn are formed; Hades, the Greek underworld (the usual Greek translation of Sheol); so also, Gehenna, the place of penal torment; and Tartarus, a term otherwise found in Greek mythology referring to a deep, dark abyss. You will find an excellent article on the matter at the OPC website under “Questions and Answers” at opc.org/qa.html?question_id=35.

Gehenna is the concept of greatest concern, as it carries the most painful ramifications, and it is the term most associated with the teaching of Jesus (Matt. 18:8–9; Mark 9:44–46). The Valley of Hinnom (source of the term) was a narrow defile near Jerusalem where refuse was burned. Basically, the fires there burned constantly. To be “cast into hell” (Gehenna) was to be punished by subjection to unceasing fire. According to the Bible, hell, as a place of punishment, is currently populated by the souls of unbelievers. These souls are not going anywhere until the general resurrection, so they will never be found roaming the earth. They are under the power of “the second death.” 

Scripture indicates that a more complete consignment to hell follows the bodily resurrection of both righteous and wicked at the end of the age (John 5:29). The righteous (who are righteous only because of the atonement of Christ) will not enter into judgment (John 5:24). But the wicked who have not turned to Christ will be remanded to eternal, irreversible punishment along with Satan and the demonic angels (Matt. 25:41).

Evidently, the departed souls of the unredeemed are “tasting” of Gehenna and can testify to the horror of it. I am thinking particularly of the uncaring rich man contrasted by Jesus with poor Lazarus in Luke 16:19–31, “And he cried out and said, ‘Father Abraham, have mercy on me, and send Lazarus so that he may dip the tip of his finger in water and cool off my tongue, for I am in agony in this flame.” The Westminster Confession of Faith, 32.1, likens this state to being “cast into hell.” Just as the souls of believers are taken to heaven (2 Cor. 5:1, 8), so the souls of unbelievers are sent to hell (Acts 1:25, 1 Pet. 3:19). “The bodies of men, after death, return to dust, and see corruption: but their souls, which neither die nor sleep, having an immortal subsistence, immediately return to God who gave them: the souls of the righteous, being then made perfect in holiness, are received into the highest heavens, where they behold the face of God, in light and glory, waiting for the full redemption of their bodies. And the souls of the wicked are cast into hell, where they remain in torments and utter darkness, reserved to the judgment of the great day. Besides these two places, for souls separated from their bodies, the Scripture acknowledgeth none.”

The adjectives “eternal” and “everlasting” (e.g., Matt. 18:8–9, 2 Thess. 1:9, Jude 7) are used in connection with the fires of hell (Gehenna). This fact leaves no doubt that Jesus and his apostles meant that the punishment would be unending. References in the book of Revelation (see above) also serve to confirm the everlasting nature of hell. Whether hell consists of actual flames or a condition that approximates being engulfed in flames is hard to tell (at least for me). Whatever it is exactly, it is clearly something to be avoided at any cost.

I trust these comments are helpful to you.