Things of interest - simple "trick"
How can we find things of interest about Agile ? How can we master Agile? Here's a trick: let's find out which are the main areas of interest and performance for the authors of Agile Manifesto, the "founding fathers":
(my apologies for possible mistakes) 
- Robert C. Martin (initiator of AM) - Design principles for OOP, Clean Code, Software Craftsmanship Manifesto
 - Martin Fowler - Refactoring, Patterns (Architecture, Design, Analysis), UML books, Technical Debt Quadrant
 - Kent Beck - XP creator, TDD, jUnit, CRC cards
 - Ward Cunningham - Portland Pattern Repository , WikiWikiWeb, the World's first wiki; Technical Debt definition; Also contributor to XP
 - Jeff Sutherland - Scrum creator
 - Ken Schwaber - Scrum creator
 - Ron Jeffries- also founder of XP
 - Alistair Cockburn - Effective Use Cases, Crystal methods, PM Declaration of interdependence
 - Jim Highsmith - Adaptive Software Development
 - Mike Beedle - Scrum consultant , applies Scrum and XP together
 - Arie van Bennekum - Dynamic Systems Development Method
 - James Grenning - invented Planning Poker
 - Andrew Hunt - book author: The Pragmatic Programmer
 - Jon Kern - co-authored "Java Design"
 - Brian Marick - Agile testing
 - Steve Mellor - contribution to UML extension and MDA
 - Dave Thomas - Co-author of The Pragmatic Programmer
 
Topics by Numbers
Another "trick":  let's count the main themes to see what matters most:
- Software design: 14
 - Agile methods & process: 10
 - PM: 2
 - Agile requirements: 2
 
It is pretty simple to master Agile, right? Just learn all these things!