Thomas Paine's Common Sense was a plain written document addressing the tyranny of the British government toward the citizens who lived in the American Colonies. It was designed to be simple enough so that the common man could read it and understand what the Revolution was about.
Most particularly, he was trying to convince those who believed that King George was looking out for the best interest of the American colonies. He goes into detail explaining the role of government in society and what government should not do in a society.
His goal was to influence more people to support the Revolution and to understand why America should free itself from British rule, America should be a separate country not part of the British Empire.
"I challenge the warmest advocate, One who argues for a cause for reconciliation, to show a single advantage that this continent can reap by being connected with Great Britain. I repeat the challenge, not a single advantage is derived. Our corn will fetch its price in any market in Europe, and our imported goods must be paid for, buy them where we will."
There were plenty of citizens who were terrified that separating from England would bring ruin to America. Common Sense which was widely read, 500,000 copies in a few weeks, was equal to millions according to today's standards of population. It spread the message of independence far and wide, read by the Continental Army, encouraging them to keep up the fight.