I've studied some fundamentals of algebraic geometry and number theory, and now I want to read papers which seem to be the "main stream" of frontier research on arithmetic.

I've heard that Mazur's "Modular curves and the Eisenstein ideal" is one of such papers (and I've also heard that it is good for people who have finished reading Hartshorne here), so I'm about to read it. But glancing through it, I feel that it goes far beyond Hartshorne, and that it needs the modular forms of moduli stack (I don't know what this is at all). And many papers on arithmetic seem to need this theory. However these papers refer to Katz's paper and Deligne, Rapoport's paper on the theory of modular forms, I feel these two papers are very difficult (and too long to start reading, not knowing if these are really good).

So my question is: Please suggest me some references on the theory of modular forms (of moduli stack? Sorry, I know nothing, except that this modular forms are not one which I'm studying in Diamond, Shurman.). If Katz and Deligne, Rapoport are the best, or these are enough to read Mazur, I tried these.

Thank you very much!