The mission of the W3C to provide the standards for the web browsers and thus, web developers have the instruction how to build their websites which code can understand any other web developer. And also through W3C standards these code is compatible for most web browsers and mobiles too.
The mission of the W3C is to guide the World Wide Web into attaining its full potential. The community also aims at ensuring that there's long-term growth of the web. You can learn more about its principles at http://www.w3.org/Consortium/.