If you don’t know what is your purpose in life, then you don’t know what you are living for. You wouldn’t have a standard to keep you doing the right things. As an article I hit upon writes, whether it is something you want to do as a job or a person, finding it is important. There is purpose behind every action. You can just have a meaningless life and do what is told to you, or you can instead have a purposeful life and do what you need to aim your dream/desire/goal/or whatever you call it. You would be able to plan and set real actions about that. If you ever think that your life is too empty, never believe that. I suggest you read this article for a brighter look.