I had one of those "aha" moments recently when looking at something about Peter's confession in a class.
After Peter confessed his faith in Jesus as the Messiah and the Son of the "living" (not lifeless like the pagan gods) God, Jesus said, "Upon this rock I will build my church. We understand the rock to be the confession of faith in Christ. The video caused me to consider something else. They were at Caesarea Philippi, a site of pagan worship, which was a huge rock that had been home to a pagan sanctuary. Jesus would destroy it and build on top of it.
I remembered reading an article about the difficulty in dating various strata in archaeological digs because when conquerors destroyed a city, they would often excavate to the bedrock before building their new buildings. Little evidence of the former occupation strata may have been left behind, leaving the impression that there was little or no occupation at all. Perhaps this is the imagery Jesus is using. Jesus would triumph and build his church on the bedrock.
The next phrase is even more instructive. "And the gates of Hades shall not prevail against it." Hades is the underworld and represents death. I don't know why this never dawned on me, but the image Jesus gives here is that the church is on the offensive rather than the defensive. A besieged city would have its gates shut up tight with folks on the wall around the gate defending it. Jesus did not say "The gates of the church would prevail against Hades," but said "The gates of Hades shall not prevail against it." It is Hades, rather than the church, whose gates are shut up tight behind the walls and besieged. The church is not hunkered down in a bunker, but is out on the offensive.
It never dawned on me that Jesus is using military imagery here! It is not the only time military imagery is used for Christ and his people (Eph 4:8-10; 2 Cor 2:14; Rev 19:11-16). Jesus is the victor on the white horse! Jesus did not intend for his disciples to dig into a bunker and build a wall around ourselves and close the gate. He desires us to get out of the bunker and storm the gates of Hades with the Gospel. Jesus confronted the dark powers with the light of God, and he wants us to do the same.
Just a few days ago, many of us did this. We stormed the gates of Hades, and we have three new sisters in Christ. We are Jesus's storm troopers on his rescue mission. Now we are planning on doing a "campaign" (another military word). A focused, concentrated effort with the Gospel will carry God's mission forward. Let us never forget, however, that the battle happens every day. We need to remember that Jesus wants us to take an offensive posture in the battle.