Celery is a great addition to the soup because it provides flavor and nutrients.  It's also lower in calories and rich in fiber, making it an excellent choice for anyone attempting to lose or maintain weight. It actually gives it a very deep, unique flavor that appeals to many people. You can also use celery leaves instead of the actual stalks for a slightly different taste.  Celery has many health benefits as well, which may explain why it seems to be a staple in soups all over the world, no matter what culture they come from.