What does "gates of hell" mean in Matthew 16:18?

You must also understand the context in which Christ was speaking. He was in Caesaria Phillipi (Banias, Israel) in front of the Temple of Pan (Ban) which was built into the rock formation... a very large rock formation. It was a very, very ornate temple, but inside the temple there was a cave where they would throw the sacrifices, sometimes children in. That cave was called the "Gates of Hades".

In contrast you see he was stating how the rock that His church will be built on will not be worshipping a fake idol, but on the fact that He is God and this paganism that they were all witnessing (Gates of Hades) will not tear His church. It was a very powerful statement and it hits more at home when you are standing in front of the Gates of Hades.

By the way, at the time Panias was like a capitol city, not just a city with a cave in the countryside, but very ornate and very hellenistic city.

I look to the Amplified version for questions like this. It says,

And I tell you, you are Peter [Greek, Petros--a large piece of rock], and on this rock [Greek, petra--a huge rock like Gibraltar] I will build My church, and the gates of Hades (the powers of the infernal region) shall not overpower it [or be strong to its detriment or hold out against it].

Matthew 16:18 (AMP)

So, Jesus is talking about the powers of hell.

An example of another metaphor like this is the image in King Nebuchadnezzar's dream. The Rock that was cut without hands hits the feet of the image, and, of course, the images does not prevail against it (Dan 2:34). Another example is the Chief Cornerstone that grinds to powder those on whom the Rock falls (Matt 21:44)

The Rock in both these examples is clearly the Christ, and I think these metaphors are all related. The gates of hell must certainly represent all of hell and death itself and more. In antiquity, the gates of a city not only represented the defenses and entrance of a city, but also important places of civil government and commerce. See Deut 16:18 and Ruth 4.

Therefore, the government of the godless (in the image of Nebuchadnezzar), the wickedness of the builders (who rejected the chief cornerstone), and place of hell itself (created for Satan and his angels), are all encompassed in the gates of hell.

In the second death, Hell and Death are thrown in the lake of fire. See Rev. 20:14. This will be the final fulfillment of Matthew 16:18.

Hell stands for hades or the grave. After death, this kingdom which we are now a part of (Phil. 3:20) will continue to stand. In other words, we are not to fear death because it (the kingdom) doesn't end there. That's why Ish. 6: 7 states,

"Of the increase of his government and peace there shall be no end,... The zeal of the Lord of hosts will perform this."

Those gates can't stay shut when it comes to something that the zeal of God is invloved in. Remember, what provoked Jesus to make this statement was Peter's confession of him being Messiah, not just Savior, but Annointed King! A king establishes his kingdom and through the cooperation of his kids (the citizens).

I believe that this passage is a metaphor based on the following; Peter > Petros = stone Petros is the feminine form of petra = solid rock, cliff or large formation. So Christ is a=saying that upon the testimony or proclamation that Christ is in fact the "Son of God", which Christ said that this revelation was not from man, but from God himself. I then conclude that the rock is this proclamation and that the Faith of peter being the value that will prevail then the "Gates of Hell" spoken about here are those things that would destroy the faith. These are the senses of seeing, hearing and thinking. These are the ways in which one who believes would begin to doubts or fears that would erode their faith. However if they are careful to protect their faith by proper discernment over what they hear, see and think, and weigh them against the believe they have come to through the "Word of God". Then these outside influences cannot prevail against the truth of the Gospel and therefore the church.

The Catholic Church has defined the Gates of Hell mentioned in Matthew 16 are heretics.

Pope Vigilius, Second Council of Constantinople, 553:

“… we bear in mind what was promised about the holy Church and Him who said the gates of Hell will not prevail against it (by these we understand the death-dealing tongues of heretics)…” Decrees of the Ecumenical Councils, Vol. 1, p. 113.

Pope St. Leo IX, Sept. 2, 1053:

“The holy Church built upon a rock, that is Christ, and upon Peter… because by the gates of Hell, that is, by the disputations of heretics which lead the vain to destruction, it would never be overcome.” Denzinger, The Sources of Catholic Dogma, B. Herder Book. Co., Thirtieth Edition, 1957, no. 351.

St. Thomas Aquinas (+1262):

“Wisdom may fill the hearts of the faithful, and put to silence the dread folly of heretics, fittingly referred to as the gates of Hell.” (Intro. To Catena Aurea.) The Sunday Sermons of the Great Fathers, Regnery, Co: Chicago, IL, 1963,Vol. 1, pp. xxiv

I've elsewhere explained in detail why Hades is translated as 'hell' in this passage, which is important for understanding it. However, in the interest of not reproducing an entire answer, I will only repost the relevant portion here.

The distinction between the Greek terms γέεννα (Gehenna), ταρταρόω (Tartaroo/us), and ᾅδης (Hades) was somehow lost in translation into the Latin Bibles and later into English Bibles. The early Hellenic, Jewish, and Christian understandings of ᾅδης are thoroughly explained in my other answer. It is my recommendation that ᾅδης be transliterated ('Hades') rather than translated (as 'hell'). With that said, this is not intended as a reference to eternal punishment in this passage, but rather as a metonymy for 'the power of death.'¹

The IVP New Testament Commentary further supports this idea that ᾅδης is a metonymy for 'the power of death':

The “gates of Hades” in the Old Testament (Job 38:17; Ps 9:13) and subsequent Jewish tradition referred to the realm and power of death; death itself would not silence the church. Against those who presuppose that Jesus could not have planned the church, though he chose twelve disciples as the nucleus of a remnant for Israel (compare the symbolic use of twelve in the Dead Sea Scrolls), the language of a “church” was already being used for a remnant community among his contemporaries (Dead Sea Scrolls...).²

The translation would thus read,

And I tell you that you are Peter, and on this rock I will build my church, and the power of death will not prevail against it.

This is a good dynamic-equivalent translation, but a formal-equivalent translation may be desirable (this is a subjective preference). For this reason, it may be preferable to translate it like so:

And I tell you that you are Peter, and on this rock I will build my ekklēsia, and the gates of Hades will not overpower it.

Jesus was essentially saying, "Nothing can stop us! Not even death!"

_{¹ cf. Biblical Studies Press, The NET Bible First Edition; Bible. English. NET Bible.; The NET Bible (Biblical Studies Press, 2006), Mt 16:18.}

_{¹ Craig S. Keener, The IVP Bible Background Commentary: New Testament (Downers Grove, IL: InterVarsity Press, 1993), Mt 16:18.}

The translation is literally, the "Gates of Hades", i.e. Death will not prevail against it. As passing through the gates of Hades would imply Death. So what Jesus is saying is that this Church will never die, it will never go out of existence.

There are no literal gates to Hell, are there?

The original Greek of the verse has Jesus speaking of Ἅιδης (Hades), and that Greek word is believed to be a translation of the Hebrew concept of שאול (Sheol), which like Hades was "the place where those that had died were believed to be congregated" (Jewish Encyclopedia).

Now the Old Testament indeed does say that Sheol has gates, e.g. in Job 17:16 (NKJV quoted):

Will they go down to the gates of Sheol?
Shall we have rest together in the dust?

And Isaiah 38:10:

I said,
“In the prime of my life
I shall go to the gates of Sheol;
I am deprived of the remainder of my years.”

The 'gates of death' are also mentioned in Job 38:17 and Psalm 9:13.

If they are not in fact literal gates in the supernatural realm, the idea must be that this is the passage into the land of the dead—i.e., actual death itself. Either way it is a one-way journey—they are prison gates which do not open from the inside—but Jesus is here giving us hope that the rock and the church built upon it will one day "proclaim liberty to the captives, and the opening of the prison to those who are bound" (Isaiah 61:1).