What contains in a Company's Mission Statement (MS)?
It is in my viewpoint that a MS of any profitable business MUST contain holistical agendas that involves all functional strategic departments in an organization. It is not enough merely to highlight the customer's value proposition or proposition to meet revenue and sales growth but it is equally paramount to structure the MS in a way that encompassess broad view of perspectives to maneuver a business by propelling all stakeholders that makes the supply chain management network.
The MS surely need not to be so detailed and complicated, rather it should be easy enough to read, understand and most of all is practical.
I opine that in order to draft the MS, business drivers ought to look from a broader perspectives of:

1. Financial Perspectives
2. Customer Perspectives
3. Internal Business Process Perspectives
4. Learning and Growth Perspectives

A MS in focus should be able to cover all the 4 perspectives above in a constructed few lines of sentences. 

An example of a MS is shared as follows,

We aim for a sustainable financial growth by being in the lead to bring customers the best value through effective product manufacturing and through developing the people assets.