Steve Reid, Composition Director 1973-1977 and 1994-1996
Focus, for me, is a term we borrowed from photography. This means we narrow something down to a very sharp image. First, it's a notion of narrowing to something, but also, it's a notion of sharpness and clarity. Focus is one of the things that clarifies purpose. So once we get a sense of thesis, that helps illuminate the photography image, illuminate what the overall purpose of the paper is.
Your purpose is why you are writing about your topic. Different purposes require different ways of focusing. Let's look at a proposal for a second ice rink in town for hockey players only.