That mission statement helps me keep the focus. For me, one of the first things is to communicate this message through writing. Another of my missions is to be a happy husband and father. It gives me clarity. When I need to make a decision I can always refer to it to make that decision.
Mission statements give mental, emotional, and spiritual clarity.
They are not as effective if they aren't written down. It keeps me more and more on track than I have ever been in my life. I am on purpose and focused on that mission. I have found this with many people I interviewed. When you get started and continue focusing on your mission you build momentum.