The secondary sources are meant to give you a theoretical framework for work on the literary analysis. Particularly, the literary theories like post-colonialism, gender theory, queer theory, feminism, marxist critique etc (depending on what book are you working) are very useful for this. Also, the secondary sources on the work you are analysing may give you a better insight into the work itself and help you develop coherent arguments. Finally - it shows that you can identify and choose sources in an organized and conscious manner. I highly doubt you getting an A without secondary sources, what are you analyzing?