I find myself writing a theoretical introduction of the type we ask of dissertators. Ha! I never thought I would do that again. But that makes me think I am writing a book on literary theory, not just a book on Lorca.
I am discussing six or seven major figures:
Heidegger and Gadamer
Borges, as theorist of translation
Benjamin on translation
Rita Felski on "Beyond Suspicion"
Not to mention Lorca.
To do it well, I have to avoid the flat explication that grad students sometimes do. What you explain is not what Foucault said, but the specific use to which you are putting Foucault. So you are still explaining Derrida, say, but you are doing so in a way that is specific to your project, not a canned summary or data dump.
So the process is quite complex. You understand the theory, you have a particular slant toward it, an interpretation that is yours, and a way you want to use it, and then you explain it in terms of your own project and in relation to other theorists. I hate the eclectic use of theory where the writer brings out several big guns but never explains what they are doing in the same discursive space.