It is written this way to emphasize what a disease really is, which is a disturbance of our consciousness that makes us uncomfortable, creates difficulties and generally makes things worse. It is based on the belief that you must adjust your thinking just as importantly as you adjust the medications you take for a illness. When we put more focus on our thoughts and the words we use, we have more control over our own consciousness instead of just repeating things that have been told to us. Separating words like is helps us to remember this.