You have to pick them at the blush stage, then ripen them off the tree. When they turn yellow and soften, they're ripe to eat.

It's my opinion that they will never be ready to eat.
But if you don't mind them, and make sure that you eat nothing but a fully ripe one, 'cause they are full of sand until they are dead ripe, they're really pretty good.
Pick them off the tree when they just start to yellow or get a bit of red on them, Wrap each one in a piece of newspaper and put them in a paper bag or cardboard box and put the box or bag in a closet . Every couple of weeks take one out and see if it is nice and soft and has a really nice pear aroma.
Pretty good when they are warm and soft and ripe.
We used to have four great big Keiffer trees, and cussed them every year when the millions of dropped fruits attracted billions of yellow jackets and their stingy little friends.
One day this woman stopped and asked if she could take some home. We helped her gather up quite a few bags and she was absolutely over joyed. She told us that Keiffer's make the best preserves and canned pears and pear butter and that she would bring us some. She told the truth. Baked Keiffer's covered in melted butter (NOT margarine) and honey is a real treat.
Canned and cooked and otherwise put up, Keiffer's make for some very good eating. Much better than any kind of pear stuff you'll ever get at the store.

No matter what you do with them, they'll always still be gritty.

I've several times read the claim that more "Keiffers" than "Bartletts" are canned and sold as "Bartlett Pears."