Perelandra shows what might have happened if Eve had not given in to Satan, while Preface to Paradise Lost shows exactly what Satan was capable of. He is the bad guy in either situation. Perelandra is a good way to look at the situation because it shows what we are capable of, even today.
While it is nice to look at the story, and understand that it would have been possible for Eve to have chosen otherwise, it makes no sense for us to only look at it in such a way because then all we do is blame Eve more for the decision she made. Instead, it would be far more helpful for us to look at it as a means to say no today. We do have the ability to say no to the temptations Satan brings our way because we are Christians and are given the ability by God. As Christians, we have been made perfect, just like Adam and Eve were perfect when they were created. It is the state of perfection that allows us to say no. Preface to Paradise Lost also gives us this option. By focusing on Satan as the bad guy, instead of Eve as the one who made a bad decision, or even as the helpless victim, we are shown that we do have strength to say no whenever we are tempted by Satan.
Because of this knowledge, these two books are immensely helpful in our Christian walk. They work in Tandem with the Bible to give us practical advice and solid examples of how we can do what God asks of us. In so doing, they empower us to live as God wants us to live, and therefore allow us to defeat Satan on a daily basis. He may be the bad guy, but he is powerless, if we choose to make him powerless.
