This is a strange one, because it gives us so few answers. I found it on "Jeff Kacirk's Forgotten English" calendar for Thursday July 25th, 2013.
Originally "churching" meant "Thanksgiving after child-birth. It was the ancient custom for the female returning to be dressed in a white napkin", according to William Carr's The Dialect of Craven in . . . . the County of York, 1828.
Okay, fair enough. A woman gives birth, goes back to church when she is recovered (dressed in a napkin because . . . ???), and she and everyone there gives thanks for the safe delivery of the child. It was probably the only time the whole community gathered regularly in one place. A church is a place of thanksgiving anyway, so it makes sense that it would turn into a tradition where everyone can give their congratulations.
However, according Notes & Queries from 1854 and then, later, Michael Denham's The Denham Tracts: A Collection of Folkore from 1895, this custom quickly evolved into (or was misinterpreted as) one of social pressure and mental abuse. Which is precisely what all new mothers need.
Denham writes that "new mothers in Northern England were once vulnerable to mysterious societal pressures until they had been churched–received back into the congregation after delivering a child. 'It is an article of the vulgar creed that if a female appears abroad [away from home] and receives either insults or blows from any of her neighbours previous to the ceremony of churching, after giving birth to a child, she has no remedy at law. Neither must a mother enter the house of friend, relative, or neighbour till she has been churched. If she is so uncanny it betokens ill luck to the parties visited'".
The problem is, they don't explain the logic or superstition behind this action. It sounds tremendously Puritanical to my ears, actually. "If you are well enough to be walking about, why aren't you at church?" Am I wrong for assuming that church services in Yorkshire in the 19th century were restricted to Sundays?
So what if you give birth on a Monday, recover sufficiently by Tuesday, and have things to do, or need supplies, or maybe just want to show your new baby to your relatives? The result is that you can't leave the house at all until you're on your way to church several days later, or else you're allowed to be physically assaulted by your neighbors with no legal recourse? What if, in their eagerness to get you back to church, they accidentally kill or maim you? What if they kill the child? It'd be your fault for leaving the house? And the bad luck thing–does giving birth somehow make you so unclean that you're just an incubus of bad luck, spreading it around to your friends and relatives? What, you go into church and Jesus says, "I cleanse thee of afterbirth and misfortune. Go forth, my child! And never again be so horrible as to propagate the species!"
I'm sorry, I think this tapped a hidden rage in me. And I haven't even had children.
I guess the moral of the story is: Kate Middleton better go to church before she takes young Prince Sproglet on his first tour of Yorkshire.