I agree totally with walker-talker and LawnLad. Only I really don't see why your lawyer insists./wants you to have on?
Heck, I was at Hertz Corporation for 14 years and we never had one. And they're a multi-billion dollar company owned by another multi-billion dollar company...Ford!
Having a Mission Satement is a great idea (don't get me wrong). But that is all it is...a STATEMENT...not a Business Plan. The two are completely different.