In other words, we need a bit of good history to read the Bible well, just as we need some linguistic knowledge to look at the squiggles on a page in the first place and recognize their meaning as words and sentences.
Value of Background
The main value of "historical background"---an expression I dislike---is that it provides us with another set of lens that keeps us from reading the text, focused only on the thought-forms, assumptions, and questions of our particular culture. Good history is medicine for the ailment of cultural "citizenization." Let me explain.
To a great extent we are all citizens of our time and place. I don't mean citizens in a national or ethnic sense---though this plays a part. I mean that the way we look at the world is shaped decisively by the key social influences in our lives, our family, education, income level, the friends we mix with, the suburb live in, the media we absorb, the Christian tribe we align with, and so on.
The process of "citizenization" is so subtle, yet so complete, that is difficult, if not impossible, for any of us to think objectively about our way of seeing reality---to discern which parts of our culture are true and good and which parts are accepted simply because we are accustomed to them.
One of the slightly disturbing things about being a student of history is coming across aspects of previous cultures that are shocking and horrible (by my standards) but which went virtually unnoticed at the time. In the first-century Roman world, we could think of slavery, infanticide, pederasty, and torture. I'm not primarily disturbed that first-century Romans failed to see this evil as evil; I'm concerned that my culture perhaps does equally horrible things that, because of my "citizenization," I cannot view clearly as sin.
If I were born in 19th-century Australia, would I really have thought twice about the fact that women and Aborigines were denied the vote? I like to think so, but I doubt it. Or if were brought up in 18th-century Britain, would I have seen anything wrong with the economically crucial trade in human lives? I fear not.
If we ponder this problem long enough, we are left with one of two conclusions about our contemporary culture. Either we have evolved to a point of cultural purity, where we have removed all blemishes of human society, or there are disturbing elements in our society that, because of our cultural position, we cannot see---elements that future generations will look back on the way I look back on 19th-century Australia, 18th-century, Britain or 1st-century Rome.
Protecting Us from Us
Here, then, is one of the main benefits of history for the reader of the Bible: Studying history protects us from reading God's Word only through the lens of the present century.
You don't need to buy into the whole postmodern perspective to admit that we all read the Bible as "citizens" of our particular time and place. I am not suggesting there is no meaning in the text other than the meaning we bring to it. But nor can we imagine that we are completely objective when we read the text. Africans spot things in the Bible that the Chinese don't immediately see; the Chinese see things that we in the West don't immediately recognize; and, of course, we in the West perceive things that African and Asian Christians overlook. The questions of one culture are different from the questions of another culture, and none of us can avoid bringing those questions to the text---nor should we.
Here is the broader value of studying history: it gives voice to the questions and perspectives of times and places other than our own. This is my defense of history when people ask, Why bother studying the past? Studying history is an act of "democracy." I'm listening to the many voices of the past rather than to the few voices of this "blip" we call the 21st-century Western world.
Every Bible reader comes to the text with a set of lenses, whether African Pentecostals, Sydney Anglicans, or American evangelicals. Knowing some biblical history gives you a second pair of lenses. To be sure, God's Spirit speaks truly and clearly to us from the pages of Scripture. He does so, however, through what the Westminster Confession calls the "ordinary means." I think most of us would understand "ordinary means" to include some knowledge of biblical language, theology, and history.
In my view, New Testament specialists ought to have a grasp of Greek language, first-century history, and systematic theology. Equally, they should use these tools to shed light on Scripture, never to avoid its meaning. The lens of history, properly employed, does not obscure the text; instead, it gives us sharper vision to see what is really there---what we perhaps have overlooked because of our cultural lenses.