What point is the author trying to make? Mortal Insturuments

In my book, the setting is a fantasy type scene. The characters have special abilities, and fight for good. They try to fight the bad off, which makes me seem like this has something to do with what they author is trying to tell us. I think the author is trying to say, do what is best. Or maybe, fight for what is right. But, during this the characters all face different struggles, and choices. So each of the choices could possibly be something the author wants us to know as well. I think the author has many different points to get across to us!