Start with Why is a really bad idea.
Start with why? Does anyone ever ask “gee I wonder *why* they’re selling this to me”? No! They want to know what the hell it is! Is it a shirt? A bomb? A toaster? What the hell is it? No one walks into Starbucks and says “why did Mr Starbucks start selling coffee? Please I must know your mission statement!”
Start with what. What is it? What are you offering? What are you selling?