Thomas Paine meant that the things we gain easily are not as valued as the things we work hard for.
Thomas Paine was quoted as writing this during the American Revolution. His writing was produced in December of 1776, an especially trying time for the American colonists.
However, Paine's writing influenced the Americans to continue to fight for independence. In this quote specifically, he is discussing how fighting for independent is not going to be easy, but it will be worth it in the end. Ultimately, Paine was stating that if this fight for independence was easy, then it would not be worth anything.