You can think and believe all that you want, but unless you share those thoughts and beliefs with others, you will not affect the world in the long term. The best way to communicate those ideas to others is to speak them. Whether you are simply having a conversation with a friend or giving a speech to a large audience, it will pass on what you have thought about to a different mind, one that potential (though not always) could spread your ideas far beyond your control. This is how we manage to live on after our deaths, for a great idea never leaves the living.