We, as being humans, are limited in wisdom, knowledge, etc.; hence, we cannot decide for ourselves what is moral and what is immoral. Therefore, a Divine Being, who knows what is best for us, decides the morality for us and this is where the religion comes into play.
Really? my friend, did you really need Islam to tell you that killing an inncocent, robbing or raping is haraam? You wouldn't have figured that out by yourself without any sort of religous influence?