The goal of modules is to support modular design. That shouldn’t be too surprising, that’s where the name modules comes from. And what that means is that if we have a large system, we can break it down into pieces. And the important thing about how we break it down into pieces is that in order to understand the whole system, we don’t need to understand all the details of all the pieces at once. We can understand each piece by itself. So to understand the red piece we only need to understand the red piece, we don’t need to know the details of the blue and the green piece. The only thing we need to understand about the green piece is the interface between the red piece and the green piece. Similarly if we’re working on the green piece. We don’t need to understand all the details of the red piece and the blue piece. We just need to understand the interfaces between the pieces.