Since  literature was born, people tried to say what it is. But literature cannot be restricted  to one definition. only.

The right definition is probably the one holding that that literature is art. When you say this, others can interprete it as they prefer.

However, literature arouses emotions. Emotions change your image of the world, they make you reflect on topics that  you usually do not consider carefully. 

Literature is an importan way to change the mind. But it does not speak with everybody's language, it speaks with uncommon words, so you can think about a personal interpretation.

When you finish a book, you can put it into an armchair and forget it, or you can reflect whether the book has changed your opinion about something.

Literature if interpreted by people that can see far away with their minds, can produce amazing changes in our world.