κἀγὼ δέ σοι λέγω ὅτι σὺ εἶ Πέτρος, καὶ ἐπὶ ταύτῃ τῇ πέτρᾳ οἰκοδομήσω μου τὴν ἐκκλησίαν καὶ πύλαι ᾅδου οὐ κατισχύσουσιν αὐτῆς. (Matt. 16:18)
And I say to you, You are Peter and upon this [very] rock I will build my Church and the gates of Hades/Sheol will not overpower it. (my translation)
Commenting on Matt 16:18, LDS apologist Barry Bickmore wrote:
The author of the Epistle to the Hebrews [wrote]; “But we are come unto mount Sion, and unto the city of the living God, the heavenly Jerusalem, and in an innumerable company of angels. To the general assembly and church of the firstborn, which are written in heaven, and to God the Judge of all, and to the spirits of just men made perfect.” (Hebrews 12:22-23). The message here is clear. “The Church” is not just an earthly organization—it existed before the foundation of the world, and it exists with the saints of all ages, both those who are on the earth and those who have passed on. Therefore, even if the Church as an earthly organization disappears and reappears periodically, the Church will always survive!
But is there any reason to believe Jesus was speaking primarily of the earthly Church? On the contrary, the text says that “the gates of hell [Greek hades = “the world of the dead”] shall not prevail against it.” What are “the gates of hades”? Hades is not hell—it is the underworld, and in early Christian and Jewish thought it was believed to be a place of waiting where the spirits of the dead, both the just and unjust remained until the resurrection . . . Thus, Tertullian (ca. 200 A.D.): “All souls, therefore, are shut up within Hades: do you admit this (It is true, whether) you say yes or no” (Tertullian, On the Soul 58). The “gates of hades,” then, represent the “powers of death” (143), and “the string of death is sin.” (1 Corinthians 15:56). Thus the text seems to be a promise of protection from the powers of death and sin for Christ’s assembly (ekklesia) of believers. For this reason Michael M. Winter, former lecturer in Fundamental Theology at St. John’s Seminary (Roman Catholic), in his excellent scholarly defense of the papacy, admits that “although some writers have applied the idea of immortality of the survival of the church, it seems preferable to see it as a promise of triumph over evil.”
Furthermore, there are numerous allusions in the early Christian literature to Christ, when he died and went to hades, breaking down the gates of Hades and leading out the faithful to glorious resurrection. For instance, Athanasius related the following tradition: “He burst open the gates of brass, He broke through the bolts of iron, and He took the souls which were in Amente [the Coptic equivalent of Hades] and carried them to His Father . . . Now the souls He brought out of Amente, but the bodies, He raised up on the earth . . .” (Discourse of Apa Athanasius Concerning the Soul and the Body, in E.A.W. Budge, Coptic Homilies [London, Longmans and Co., 1910], 271-272). Therefore it is clear what Jesus was talking about when he said “the gates of hades” would not prevail against the Church, and to apply this statement to the perpetuation of the early Church would make no sense. (Barry Robert Bickmore, Restoring the Ancient Church: Joseph Smith and Early Christianity [rev ed.; Redding, Calif.: FairMormon, 2013], 48-49)
Elsewhere, Bickmore offers an alternate interpretation by another Latter-day Saint:
An alternate opinion was expressed to me by one of the reviewers o this book. In his view, this passage refers symbolically to the earthly Church, but the phrase, “the gates of hades shall not prevail against it” suggests that the Church would at some future time be located behind the gates of hades, but would not remain there. Thus the passage is actually a prediction of the future apostasy and Restoration. (Ibid., 322 n. 146)