In this quotation, Paine talks about the "summer soldier" and the "sunshine patriot." When he talks in this way, he is referring to people who offer support but not at any personal cost to themselves.
These are the soldiers who would most likely shrink from the service of their country. This means that they would most likely not fight when necessary. By using such positive words, Paine implies that these soldiers are only willing to fight as long as conditions are good and they do not have to suffer much.