Anyway, this led us to a stray line from Donne's sermon preached before Charles I at Whitehall on 1 April 1627 (as a new war with France was heating up):
In this Church, [God's] ordinance is ordnance: his ordinance of preaching batters the soul, and by that breach the Spirit enters.
Get it? Preaching is God's weapon, God's cannon, used against our own souls, to break them open the way cannons breaks the city wall -- and send in the Spirit as an invading and occupying army. He goes on to say that "[God's] ministers are earth-quakes, and shake an earthly soul." There's quite a bit more in that line as well.
Not, we say again, imagery for all times and places. But worth meditating upon before one stands up to preach.