I have seen this behavior in kittens before who are nursing with the mother. They push and pull on the mother's fur with their paws to get the milk. My cat, however, is a adult and has no mother. She does this while purring loudly and it seems to make her happy. Is this is memory that she is re-enacting? Is it a self-soothing behavior? I know little about her before I found her and her siblings abandoned, seven years ago. She was very hungry back then.
"In adulthood, a cat supposedly will knead when it's feeling happy or content because it associates the motion with the comforts of nursing and its mother. Adding further weight to the explanation: Some cats even suckle on the surface they're kneading."
When it comes down to it though, no one knows for sure why exactly some adult cats knead.
Humans' domestication of cats has caused them to retain many childhood actions and habits into adulthood and kneading (as in kneading bread) is thought to be one of them.
As you know, kittens knead at the mother's teats to cause lactation (the flow of milk). Can you imagine something better than being up close to Mom, all warm and cosy, getting delicious milk?
When an adult kneads, he or she is demonstrating an activity which was pleasurable for them in kittenhood and still gives them pleasure.
We have had kneaders that are so into it that I've often wondered if there is a way to get them help me knead the dough when I make bread.