Paine opens the pamphlet by admitting that the ideas he's about to lay out might not be incredibly popular at the moment (i.e. the summer of 1776). But he's confident that once people have had a chance to digest his arguments, they'll see that independence from the British is the only way for America to move forward.
Paine continues by insisting that the cause of American independence affects more than just America. The whole issue of tyranny and absolute power (like the kind held by the King of England) is something that affects almost every country in the world, and Paine hopes that America will one day become a shining example of democracy and freedom to these other countries.
Finally, he concludes his short intro by saying that he has chosen to publish this text anonymously because he thinks that his ideas should stand for themselves. In truth, he's also probably worried about getting arrested by the British.