Kneading is a very common behavior for cats. It may just be soft pawing or even a repetitive clawing. Regardless of when or where, if a cat feels the need to knead, they will. Why do cats love this activity so much?
Kneading represents a period of comfort and safety. During the nursing process, kittens will knead their mom's belly to increase milk flow. Kneading then becomes an instinctive behavior that they carry with them past kittenhood. Its a moment of happiness and contentment. Much like certain food or activities remind you of childhood, kneading brings your cat back to a comforting time.
Your cat is marking their territory.
Kneading is also a way for a cat to create a safe space. Cats have scent glands on the pads of their feet, and these produce a unique scent. A cat releases this scent to claim territory and define what is theirs. They may also claw to leave signature scratches on something they want to mark as theirs. So, next time your cat is kneading on your lap, consider it a compliment!
If you don't like your cat's kneading behavior...
Consider redirecting your cat to an area besides your lap. You can simply reward your cat for kneading in a certain area - maybe a blanket or pillow. It is important to remember that kneading is a normal and comforting activity for your cat, so you shouldn't discourage the behavior.
Now you know why your cat needs to knead. Next time you witness this behavior, you can understand a little better why your cat enjoys it so much!