No, not just a door- an 11th century door.
And not just a 11th century door but one with ironwork that represents Ragnarok- the Norse Doomsday.
In a Christian Church? Well there's a cross at the top so that makes it alright. Savvy?
So... The big circle on the left is the Midgard Serpent and the shapes on the right are the serpent after Thor has smashed it up with his hammer. The circle in the middle is Surt, the Sun Wheel and the dragon flying across the top is Nithoggr the eater of the dead.
The thing in the bottom left hand corner that looks like a long-necked bird might (though I'm not convinced) be the cock whose crowing announces the end of the world.
The door isn't in its original doorway and may well have been brought to Staplehurst from somewhere else. The only comparable piece of work is at Stillingfleet near York.
(Most of the information for this post comes from Anita Thompson's Brief History of Staplehurst)