I presume you mean in Java??
Well, Exception is a generic, abstract exception class, and RuntimeException is an abstract subclass of Exception (RuntimeException itself is never thrown, only one of its subclasses such as NegativeArraySizeException).
If you mean, why bother making a distinction between Exceptions and RuntimeExceptions when all of RuntimeException's subclasses could inherit directly from Exception, it's because it's useful to group exceptions so you can catch several at once instead of having to catch a big list of them.
Btw, I realise that Exception and RuntimeException are not technically abstract classes, as their methods have an implementation, but they are abstract in the sense that they do not describe specific exceptions.
I hope that's somrthing like the answer you wanted, but it was a very unclear question...