The Bible says the Lord knows who are His, and those who are His are among those who profess to believe in Him. Now, I believe you mentioned the passage in which Jesus, speaking of the Church, sas the gates of Hell won’t prevail against it. But when people say or are identified as Christian, but aren’t, then Hell has prevailed over them. So it is not a church as an earthly institution that’s meant, for they include both wheat and tares, but those whom the Lord knows as His.
Gates are defenses. Gated communities, the gate that separates your front yard from the public sidewalk, the gate on the bank vault, etc.
I am not at all sure of the meaning of the passage but it may well refer to hell not being able to successfully the forces of God. Would this be a reference to Armageddon? I don't know. I am no expert on Scripture. However, I had always thought of those gates of hell as offensive weapons to be used ineffectively against Christians which simply goes to show my obtuseness regarding my errors as to at least some Scriptural meanings.
I do agree that all churches have wheat and tares but it is not the institution that goes to heaven or hell but the individual. There are some folks who claim to be Catholic and who believe somehow that only Catholics go to heaven at least ordinarily. They follow teachings of the early Church Father St. Cyprian of Carthage that "outside the Church there is no salvation." In later times. numerous popes and the Catechism of the Catholic Church have explained the actual complexity of this teaching as meaning that those who go to heaven get there in some way via the Catholic Church.
When Jesus Christ was being crucified, there were two others being crucified: the good thief and the one who was not so good. The good thief is traditionally known as Dismas. When the not so good thief challenged Jesus to the effect that if Jesus was really Messiah, he should save the three of them from crucifixion. Dismas rebuked the not so good thief by asking Do you have no respect for Him even at a time like this? Jesus, remember me when You come into your Kingdom. Jesus assured Dismas that Dismas would on this day join Jesus Christ in heaven Luke 23: 39-43.
There is also that part of the Creed which says that after His death, Jesus "descended into hell." Traditionally this is believed to mean that he went to the place of the souls of the dead, all the dead, and opened heaven to those who had lived righteous lives. They could not enter heaven before His actions had saved them.
Now, as I have said, I am no expert on religion, mine or anyone else's. Take the foregoing as you will as all of us search for the Truth.
May God bless you and yours.