I have never really concentrated on Langlands, which explains my poor level of understanding of it. But I have read quite a few introductory papers related to Langlands, and to the circle of ideas surrounding it. I finally feel like I know what it is I don't know, and I can finally articulate what I need references for.

The following phenomena/processes are mysterious to me:

- My understanding is pretty vague when it comes to direct integrals. I would like a reference that would explain their importance in understanding representations.
- While I have done some reading about reductive groups, and linear algebraic groups more generally, I am still very vague about the intuition behind parabolic subgroups, and why they should be related to cusp forms. As I understand it, the definition of cuspidal representation is that there exists a central representation $\omega$ such that the given representation is an irreducible unitary subrepresentation of $\{f|f\in L^2(Z(\mathbb{A})\mathbb{G}(K)\backslash\mathbb{G}(\mathbb{A}),\omega), \forall K$-parabolic subgroup $\mathbb{P}$ of $\mathbb{G}$ the integral $\int_{N(K)\backslash N(\mathbb{A})}f(gn)dn$ is equal to $0\}$. I don't at all understand how this relates to cusp forms, and how I should be thinking of parabolic subgroups. I would love a reference that gives intuition about this. At the moment "parabolic subgroup" is a completely technical definition, as far as I'm concerned.
- I understand that Eisenstein series can somehow be thought of in terms of scattering theory. (Some theory in physics about how lines scatter in manifolds?) I don't understand any of this, and I would love a reference that would put Eisenstein series in their proper context, in a nice, readable manner. All I know about Eisenstein series is their definition in the classical modular forms case, and that somehow they are related to the continuous spectrum of $L^2(Z(\mathbb{A})\mathbb{G}(K)\backslash\mathbb{G}(\mathbb{A}),\omega)$, but I really don't understand the process or the philosophy...
- I don't understand what is meant by "cusp form" in general. I certainly know what a cusp form is in the classical modular forms case, and I know the definition for (though, not the intuition of) cuspidal representations for general reductive groups, but I don't know what is meant by "cusp form" for a general reductive group... I'm given to understand that they're supposed to somehow be related to embeddings into projective space, just like sections of very ample bundles? I would love a reference that explain some of this context.
- I have read about spherical Hecke algebras, and the Satake isomorphism. I know that L-functions of automorphic representations are given by the Satake parameters, which are given by the Satake isomorphism. This definition seems extremely unnatural and contorted to me! Do you have a reference that explains why it is natural to construct L-functions in this way?
- Anything that has to do with the word "growth" is unfamiliar to me: "rapid decay", "slow growth". I know that these notions are somehow important, but I managed to never understand their importance... What is a reference that explains the intuition behind caring about growth, and how it relates to the bigger picture?
- All of the above was on the automorphic side. This request for a reference is on the motivic side, or, at least, about the Langlands correspondence itself. The Local Langlands conjecture (theorem!) for $GL_n$ says that there is a bijection between the set (class?) of smooth, irreducible, complex representations of $GL_n(F)$ and equivalence classes of $n$-dimensional semi-simple Weil-Deligne representations. The definition of "semi-simple Weil-Deligne representations" is quite technical! I don't understand where this definition is coming from, and why that is the reasonable thing to consider. Is there a reference that explains the context in which this definition arose, and why it is a reasonable thing to consider?
- As I said in question 7, the Local Langlands for $GL_n$ gives a bijection between the set of smooth,
**irreducible**, complex representations of $GL_n(F)$ and equivalence classes of $n$-dimensional semi-simple Weil-Deligne representations. What would irreducible semi-simple Weil-Deligne representations corrrespond to? Cuspidal representations? (I think I heard that once.) Why? Where can I read about the intuition of this?

I asked for references for a lot of things. I'm sorry if that is inappropriate. I'm new to the site, so I don't know the proper etiquette yet. I feel like things are finally falling into place for me about Langlands, but that I'm still extremely rough around the edges. I thought that this would be a great opportunity for me to get some leads about what I should read next.

I should mention that I have a huge preference for texts that give intuition. I would also prefer expository papers to books, just because it's easier for me to go through. But if you think that the best explanation is in a book, then please write that.