The same way that a company's mission statement defines its purpose, a brand's mission statement defines its values.
The tricky part, however, is that value is subjective. It differs from person to person and often depends on what that person is looking for in life and what problems they're trying to solve at any given moment in time.
A good brand understands this and knows that it has to speak to these values if it wants to build an audience.
Yet, many brands want to be noncommittal when speaking to these values because they don't want to alienate any potential customers. But by being noncommittal, they end up alienating the very people they stand to help the most because those people can't tell if what's being offered is for them or not—the brand isn't speaking in a way they value.
If you want to build a strong brand, you need to speak to the things your customers find valuable. You can uncover what a person finds valuable by understanding the problems they're trying to solve. Talk to enough people and you'll start to find groups that are tackling the same problems. It's the brands job to find those groups, speak to their problems and offer a better way forward.