This chapter is about the absurd notion that a nation should desire to have their exports exceed their imports as much as possible. And I really can do anything to clarify it any better than to reiterate what Bastiat pointed out at the end of the chapter, which was simply taking protectionist logic to its finishing point.
By this logic, a nation is made better by passing its goods through the customhouse and then tossing them into the sea. And inversely, a country would be made poorer is another nation gave them goods and products without asking for any in return. Try to make sense of that?