I suppose we all like those movies that have twists in the end. Some of them you can see coming, and other movies make it a goal to hide it from you, and you are completely shocked at how it turned out. I can think of dozens of movies where I was completely surprised. Of course, some of M. Night Shyamalan's movies qualify here (some as more surprising than others). You might be surprised to know that the more one studies the Bible, the more you might find that it says something very different than you thought it did.
When I was a young student in John Walton's Hebrew Exegesis class at Moody, I was first introduced to the idea that words have limited meaning and they do not carry their context. I learned this not only in theory by reading the thousands of pages Dr. Walton had us read, but also because he made us practice the lexicography about which we had been reading by writing a paper that analyzed a particular word each week.
This was incredibly valuable for me in the long run, as it caused me to understand how written communication actually works. It was one thing to learn Greek or Hebrew, but it was quite another to learn what one can and cannot do with them. In fact, I truly believe that much of the disagreement between theological positions and diversity in interpretation has to do with the fact that many people are just applying fallacies of interpretation that do not take contextual factors into consideration.
Virtually every trained scholar now agrees with the above in theory. The problem is that many today do not apply this logic to source analysis in the Bible. It is argued that the Bible teaches such and such a topic, but when one looks to the argument as to why it teaches such, the argument has to do with what it once may have taught in another context.
You see, the reason why diachronic or etymological information is of limited value when analyzing each individual occurrence is because words, phrases, sentences, paragraphs, and entire works that may be incorporated into larger contexts no longer necessarily carry their implicatures over into that new context. In other words, reference cannot be carried. It can be duplicated if that new context allows, but if the context is different then the reference will be different.
Hence, arguing that the Bible teaches one to sacrifice children, for instance, when in fact that is an argument from different things that are said that may have once functioned as such in a different context is bad scholarship, simply because it commits the same fallacy that one commits when he tries to carry a contextual reference with a word over to a new context.
Let's actually assume for a moment that the phrase in Exodus 22:29 that "You shall give to Me your firstborn sons" actually meant in a previous context that people were to give YHWH their firstborn sons in literal sacrifice. All scholars now admit that such is qualified now in the context to mean sacrifice via dedication. The larger contextual references make that clear now. Because of this, it is fallacious to argue that because a source may have once said X that it retains that reference in its new context and therefore the new source teaches X. In fact, it does not. With its new referents, it teaches Y, not X.
The same thing can be said for scholars who argue that the Bible's use of polytheistic language evidences that the Bible teaches polytheism. Again, this is a complete and utter misunderstanding of how language functions. In a polytheistic context, polytheistic language has the implicature, "other gods exist." But in a monotheistic context, that implicature no longer exists. Hence, the statements function as idioms to convey something different in terms of their implicatures in a monotheistic context. The current debate around these passages likely does not take into consideration this fact. In fact, even in an atheistic context, polytheistic language can be used (e.g., "Tyra Banks is the goddess of fashion," "That woman is such a diva," etc.). No one believes that the literal implicature carries and that the person who utters the above phrases evidences some assumption that goddesses literally exist). Implicatures do not necessarily carry because reference does not carry. Hence, one must study whether the larger biblical contexts teach such implicatures or not, and of course, for orthodox Christians, the canon as a whole now functions as a larger context as well to its smaller components, such as books, larger traditions, and pericopes within those books.
Now, this doesn't mean that diachronic data is worthless. It's interesting to note whether the synchronic information is in continuity or discontinuity with the linguistic element's previous context(s); but it can never just assume one or the other based on the way it was used elsewhere.
My hope for the future of scholarship is that, as many return to a belief in source analysis (and such is interesting for history as well as the above), it would apply what it already knows to be true with smaller units of language to larger phrases and source material. Only then are we going to see a fruitful use of such data. Until then, we're going to get a lot of confused students arguing that the Bible teaches X to a lot of confused laymen who will now believe the Bible teaches X when, in fact, it teaches no such thing. In fact, we may find that rather than teach X, it may teach -X. Wouldn't that be quite a twist at the end?