What does "nothing to write to the bishop about" mean? Even really fasting, it is your won business

Nothing to do with the bishop at all. It's something of passing interest, but nothing to write home about, which is the more common expression.

nothing to write to the bishop about & nothing to write home about

both mean "X is not very important at all".

Well gentlemen, I didn't get you very well.
Did you mean "I know – nothing to write to the bishop about – but it's a good way to remind myself that my hands do still work" means "I know – in a whim – but it's a good way to remind myself that my hands do still work"?

I don't understand what you mean, above, Ori.

"nothing to write to the bishop about" & "nothing to write home about"

both mean "X is not very important at all".

Ori: I won some money in the lottery. But it was nothing to write home about.

Ori: I won some money in the lottery. But it wasn't very much so I won't bother to write my parents/brothers and sisters about it.

Got it.
That explained the mysterious X, JTT.
Thanks.