What is the point of introducing sheaf, line bundle and all the strange terminology in modern algebraic geometry ? I had to learn some bits of this by myself (books, articles on my subject, etc) and I still have a hard time to see what it brings to the overall things. For example I'm working on abelian varieties right now, and I came across a paper that make extended use of theta structures, amble line bundle and so on. And I feel it's only obfuscating the point of the authors (which is presenting a efficient arithmetic on Kummer surfaces). So, can someone give me the intuition behind the vocabulary ?