[pilgrim]

In Matt. 16:18 the Lord had said that He would build His assembly, “…and the gates of Hades would not prevail against it.”
He was about to be crucified and was only encouraging His disciples by saying though He was to die, yet the grave would not hold Him (the gates of Hades would not prevail against His building His kingdom assembly that He and they had offered but had been refused). He would rise from the dead and yet build it.
The gates of Hades had nothing whatever to do with the preservation of the present church or kingdom assembly (ekklesia). The point made by the Lord was, Hades would not prevent Him from building His kingdom promised in all the prophets from the foundation of the world because He would rise from the dead (Hades).
That was what He came to do in fulfillment of the Scriptures. Among a host of Scriptures saying the same, Psalm 89:3-5 says:

I have made a covenant with My chosen, I have sworn to My servant David: ‘your seed I will establish forever, and build up your throne to all generations. And the heavens will praise Your wonders, Lord; Your faithfulness also in the congregation of the saints.

One of the most common mistakes is the belief that when the Lord said the gates of Hades would not prevail against “it” that He was speaking of the present church, viz., that Hades would not overcome the present church. If we keep things in context and remember the subject concerned the sure establishment of the kingdom of heaven that He gave Peter the keys to open, a simple question can settle the matter.
What does Hades have to do with the present assembly? In what way could Hades overcome the church? There is no communication or connection between the two. The souls of people or demons there have no authority or power to affect anything on earth. Hades after the cross is a prison only for the lost (Zech. 9:11-12, Lk. 4:18) created by God for the confinement of the wicked awaiting the great day of His judgment that He only controls.

In His grace

pilgrim