It is not a metaphor for error, it is an actual place of pagan worship at Ceasarea Philippi:
http://www.youtube.com/watch?v=nx6jjjgrymo
So the context of that conversation in Matthew 16 is usualy misunderstood. The "gates of hell prevailing" does not imply the church would fall into error, it was a reference to the lies of paganism & how those errors would not prevail against the gospel.
The Jews speak of the gates of hell: sometimes of the gate of hell, in the singular number {p}; and sometimes of the gates of hell, in the plural number. They say {q}, that
"Mnhygl vy Myxtp hvlv, "hell has three gates", one in the wilderness, one in the sea, and one in Jerusalem.''
They talk {r} of "an angel that is appointed Mnhygd yert le, "over the gates of hell", whose name is Samriel; who has three keys in his hands, and opens three doors.''
And elsewhere {s} they say, that "he that is appointed over hell his name is Dumah, and many myriads of destroying angels are with him, and he stands
Mnhygd axtp le, "at the gate of hell"; and all those that keep the holy covenant in this world, he has no power to bring them in."
:world, he has no power to bring them in.''
Our Lord may allude to these notions of the Jews, and his sense be, that all the infernal principalities and powers, with all their united cunning and strength, will never be able to extirpate his Gospel, to destroy his interest, to demolish his church in general, or ruin anyone particular soul that is built upon him. Again, the gates of "Hades", or hell, sometimes seem to design no other than the gates of death, and the grave, and persons going into the state of death; see
Job 38:17 where the Septuagint use the same phrase as here; and then the sense is, that neither death, nor the grave, shall finally, and totally prevail over the people of God, and members of Christ; but they shall be raised out of such a state, and live gloriously with him for ever. By it here is not meant Peter himself; though it is true of him, that Satan, and his posse of devils that beset him, did not prevail against him, so as to destroy his grace, hurt his estate, and hinder his salvation: nor could death, in all its frightful appearances, deter him from holding, and preaching, and maintaining the doctrine of Christ; and though death, and the grave, have now power over him, yet they shall not always detain him: but rather, it designs the doctrine Peter made a confession of which, , though it may be opposed by hell and earth, by Satan, and his emissaries, by the open force of persecutors, and the secret fraud of heretics, it may be brought into contempt by the scandalous lives of professors; and though the true professors of it may die off, yet truth itself always lives, and defies the power of death, and the grave: or else the church in general is meant, and every true believer. These words do not ascertain the continuance of anyone particular congregated church, but secures the church universal, which will continue as long as the sun and moon endure, and the perseverance of everyone of God's elect; and assure that death, and the grave, shall not always have the dominion over the saints, but that they shall be rescued from them. Once more, this "it" may refer to Christ the rock, who, though he was brought to the dust of death, by the means of Satan, and the powers of darkness, yet to the ruin of him that had the power of death; and though death, and the grave, had power over him for a while, yet could not hold him; he rose victorious over them, and ever lives, having the keys of hell and death, to open the gates thereof, and let his people out when he thinks fit.
{p} T. Bab. Sabbat, fol. 39. 1. Succa, fol. 32. 2. Bava Bathra, fol. 84. 1. {q} T. Bab. Erubin, fol. 19. 1. Menasseh ben Israel, Nishmat Chayim, fol, 33. 1, 2. {r} Zohar in Gen. fol. 47. 4. {s} Ib. fol. 7. 1.
-from John Gill commentary[SIZE=+1]
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