“On this rock… the gates of Hades shall not prevail”
And I tell you that you are Peter, and on this rock I will build My church, and the gates of Hades will not prevail against it. (Matthew 16:18 BSB)
What it sounds like today
Hell's armies attacking the church, with 'gates' as an odd weapon.
The cultural key
A wordplay first: 'Peter' (Petros) and 'rock' (petra): in the Aramaic Jesus spoke, one identical word, kepha. The scene is Caesarea Philippi, beneath a massive rock cliff housing the grotto of the god Pan, a cavern with a spring popularly treated as a passage to the underworld (a vivid backdrop, though the connection to the saying is a modern interpretive suggestion). 'Gates of Hades' is old biblical idiom for the power of death ('the gates of Sheol,' Isaiah 38:10), and gates are defensive architecture: they don't attack, they hold.
Recovered meaning
Death's stronghold is the thing under siege, not the church. The image is the church advancing and death's gates failing to hold it, inverted from how the verse is usually heard.