Reading the Bible is often like entering a movie in the last fifteen minutes. You pretty much have no clue what has been going on, and instead, tend to speculate what the movie was really about. The reason why this is the case is because we are reading a text that is written in a language which references a world that is not our own. That's why assuming that a passage is literal before knowing the conceptual referents of the language you're reading is a really bad idea. It's only meant to be literal if the author would have understood it as such, and that itself can only be accessed through context.
Context understands words within their literary environment (i.e., within other words in morphological and syntactical relationships) that extends from collocations to clauses, clauses to sentences, sentences to paragraphs, paragraphs to pericopes, pericopes to books, books to sections of books, sections of books to canon, etc.
But part of the context is the cultural context because it too contains concepts to which the authors words refer. For instance, the word "heart" in the Old Testament and certain parts of the New (specifically the Synoptics) refers to the seat of thought in the ancient Near East, but we tend to read it as the seat of emotion and good intentions. Without the ANE background, we lose the real meaning of the word. Often this means that we are merely getting right teaching from the wrong texts, but there can also be cases where we get the wrong meaning from the wrong texts.
So knowing ancient Near Eastern texts are vital in understanding the concepts to which certain words or phrases refer.
But what does this say to the Reformed doctrine of the perspicuity of Scripture, i.e., the doctrine that teachings that Scripture is understandable to everyone who reads it?
First, as I said before, right teaching from the wrong texts is often a result of not getting the original referents of a text. The Holy Spirit is promised to bring His people into all truth, not give them omniscience to know everything about a text. Hence, it seems the case that He has, throughout history, merely used whatever hermeneutic of a given religious culture to interpret the Bible for that people and make Christ known to them.
Second, and this is an important point to make, the doctrine of perspicuity does not refer to everything the Bible teaches, but rather to the general understanding of the gospel story. In other words, it is the main story, the narrative that moves us from creation to new creation that can be understood by any Christian.
That brings us to the third point. The doctrine is discussing what every Christian can understand about what the Bible teaches. Hence, not every unbeliever or heretic will understand it. It exists to confound the unbeliever, so that while seeing they do not perceive, and while hearing, they do not understand.
This creates a balance for every believer. He is both dependent upon his "disciplers" who watch over his soul, the shepherds and teachers, the evangelists, etc. to feed him; and yet, he is held responsible for following Christ through the Bible, a responsibility for which he must give an account for what he has decided. He, therefore, both needs the church, all the while being held responsible to seek God through Christ himself. He is both priest and in need of a priest at the same time. He is an individual in need of family and belongs to a family in need of him.
When we discuss the need to understand the background of a book, therefore, no one should hear that as "the Bible is incomprehensible without understanding its background." This simply isn't true, as the literary context is primary and often written in such a way as to lend itself to some truth, even if it is a different one that the author originally intended.
For instance, the Epistles of John can be understood just fine without an appeal to its background; but once the background comes into our knowledge, we see the text in fuller color, often understanding the richness of what was being conveyed. Hence, the readers of John have no need of a teacher when it comes to the big picture stuff (i.e., the gospel and love that should come forth from them because of it), but they are in need to bring themselves under teachers so that they have fellowship with God through apostolic doctrine.
So seeing the ANE background as helpful for the purpose of interpretation is not contradictory to the doctrine of perspicuity, since the basic story of the Bible has been understood for the past two thousand years without it. But it does give us more context, and as such, aids teachers to teach texts in fuller color, correct misconceptions, and link right teaching to the right texts.