I tried Barbara Pym when I was younger, and I really just did not "get" her. I then re-read her when I was a bit older, and going through a different stage in my life - and everything fell into place. That is really how I would describe it: I suddenly "saw" the humour, the subtle observations, the perceptiveness.
You have to believe that her (main) characters have a degree of self-knowledge (along with blindness), and that they are not sad, hopeless losers. I think with that in mind, it all begins to make a lot more sense.
She is very subtle. She doesn't provide the reader with huge pointers as to how to read her books.
I am a bit annoyed because I can't remember the name of the book I read that helped me make sense of her. It's the one where the young student has just moved out of his writer-girlfriend's flat, in a slightly selfish manner. She's a writer-journalist, and older, and she typed (and probably edited heavily) his thesis.
Once you realise that Barbara Pym was quite like that character, her other writing makes a lot more sense (well, it did for me, anyway).
"A Glass of Blessings" is far and away my favourite, too, scone. It is quite sad. There is a terrible, appalling existential pain at the heart of the book, which it circles, and never, ever names. All the lightness, the trivia, is there precisely to demonstrate how unspeakable this pain and sadness is - and how we humans can't even talk about this awful tragedy (death, aloneness, the vacuity of human existence).
It is very funny. It's also stylistically quite bold, in that it risks a heroine who might seem an absolutely vacuous idiot, with no self-insight and a great deal of blindness concerning others - and it offers very little to gainsay that opinion. But, if you accept that there are reasons for the things-which-are-not-said, you begin to see her silences on the "deep" things - love, loneliness, the purpose of existence, the task of living, relationships with other, fidelity, commitment - as a kind of stoicism: and one made particularly poignant precisely because it is never acknowledged (by others) as such, and is easily mis-read, or overlooked.