No, that's not really necessary.
It's a good idea to use the
JLS to find out exactly how something works if you don't understand it, but I don't recommend trying to read the whole JLS from front to back - it's a very technical and detailed document.
If you're studying for SCJP, I think it would be a waste of time to try and understand the whole JLS - you'd better concentrate on the topics that are relevant for the exam, do mock exams to discover where your weaknesses are, and study more on those.
Books such as
K&B are much more practical when you're preparing for the SCJP exam.
[ June 06, 2008: Message edited by: Jesper Young ]