Summary: The church doesn’t exist to protect the camp; but to move against the foe.
“…I will build My church; and the gates of Hades shall not overpower it”
This statement by Jesus, in context, is a response to Peter’s confession of Him as the Christ, the Son of the Living God, there in Matthew 16:16 (quickview)  A proper exegesis of this passage would have to include the whole passage, from verse 13 through 20. And there is much to be said from this account of Jesus’ challenging question, put to His disciples.
But this one phrase we study today is so powerful, that it stands easily on its own as one that the church of the 21st century cannot afford to ignore, and the Christian of the 21st century cannot afford to be ignorant of.
So we will lower the glass on this one phrase today, searching carefully to detect what it is saying to the church, and to the individual who claims to follow Christ.
May God, by His Holy Spirit, both convict and bless our hearts with His truth, spoken out of His own mouth and then inspired by His Spirit to be recorded for us who hear it today.
YOU ARE THE CHURCH
Jesus said, “I will build My church”; and as was already pointed out, the foundation He referred to on which He would build this church was the truth of who He really is. The Anointed One of the Living God; indeed, His very Son. No less. Not Elijah. Not Moses. Not one of the great prophets. But the Promised One. The One spoken of in the Garden of Eden, who would crush the serpent’s head.
The church is built up on settled conviction and assurance in the hearts of His people, that He is the Christ and the Savior of the world.
So what is the church? It is you. It is every man woman and child in history, from beginning to end, who come by faith and place their trust in Christ’s shed blood for salvation, and His resurrection for life. If that describes you, then you are the church.
Jesus said, “the gates of Hades” would not prevail against the church.
One commentator gave this application to this verse:
and the gates of hell—“of Hades,” or, the unseen world; meaning, the gates of Death: in other words, “It shall never perish.” Some explain it of “the assaults of the powers of darkness”; but though that expresses a glorious truth, probably the former is the sense here. - Robert Jamieson
Commentary Critical and Explanatory on the Whole Bible (1871)
Let me translate that just a little for you. This author is saying that since reference to the gates of a city imply its strength, and the strength of Hades is death, then what Jesus is saying is that He will build His church, and death, the power of Hell, shall not be feared by the church because it cannot prevail over her.
Now there is some validity to that application. In Hebrews 2:14 (quickview) ,15 it is revealed to us that Christ took on flesh so that through death He might render powerless him who had the power of death, that is, the devil; and might deliver those who through fear of death were subject to slavery all their lives.
So in that sense, the power that Hades has over men is broken, when one believes the gospel, enters into the family of God and no longer fears death because he now has eternal life.