As some of those before me have stated, the document is ever changing and being updated. I've been using it since about 1979, and I am constantly surprized that "Facts" that I absolutely KNEW were in the code, are no longer there, or completley changed.
To further complicate things here in California, we have a State of California Electrial Code, (CEC-Title 24 Part 3), which consists of the NEC with State Amendments, so we have two versions of the code. Our current version is the 2007 CEC which consists of the 2005 NEC with 2006 State Amendments. Very confusing to those not used to the system. I would venture to say none of us will "master" the book. We can learn to navigate it efficiently. Know where to find specific areas of information. For example I use Article 517 extensively as we do a lot of health care work. But I never expect to master the entire document.
Take a course, use the Handbook and learn the specific areas you use extensively and you will be a step ahead. Talk to Inspectors, plan checkers, experienced electricians, and you will further your understanding.
Good luck, oh, and by the way..., this forum is a great resource. Some of these gentlemen have forgotten more about codes than I have ever learned.