There's a verse in 1 Corinthians which tells us a bit about how to understand the Bible. It is interesting that what it says actually goes against at least two commonly held beliefs by some people who teach theology and stuff. Of course, there are about as many opinions as there are theologians...
Now these things happened to them as an example, but they were written down for our instruction, on whom the end of the ages has come.
1 Corinthians 10:11, ESV
False Statement 1 - Theology and History are Separate
"These things" refers back to what Paul has just been writing about - specifically details of the Exodus and the Israelites wandering in the desert that had happened over a thousand years before. There is a tendency in liberal theological circles, thankfully starting to die out now, to say that if something has theological value, it doesn't also have historical value. So people argue that because Jesus turning water into wine is a picture of him replacing the temple (which it is), that means it didn't happen, because the theological point is a good enough reason to record the story.
That is of course complete rubbish, because the theological truths also need to have a correspondence to reality. If Jesus did not rise bodily from the dead, then the "theological point" that is made by the accounts of his resurrection is false. In order for the theology to be valid, the history needs to be valid as well. (Yes, there's a whole load of stupid arguments among some German scholars ages ago about what the meaning of history is. They are stupid. I'm using "history" in the sense of "events that really happened in the past".) That's a point that has been well made in a lot of the New Testament stuff by NT Wright, and others.
Paul's point here is that the events of the Exodus took place as examples. They took place. And they did so as examples - both the theological and historical are true, and indeed need to be true in order for them to be valid examples. Yes, there are cases (Jesus' parables for instance) where things do not have to be true in order for them to be valid examples. That isn't the case here.
False Statement 2 - The Importance of Original Meaning
One of the most commonly taught ideas in the whole area of how to understand the Bible is the idea of the importance of original context and original meaning. The main meaning of a passage is what it meant for its original recipients.
The problem is that what Paul says contradicts it. It doesn't contradict the idea that original context is often very important for understanding the passage, or that the original significance for the readers is important. But Paul says that the events recorded in Exodus happened and were recorded "for us". Why? Because the "end of the ages" has come - which in Paul's theology refers to the fact that Jesus has come - that all the ages were pointing to what happened in Jesus. Paul sees the main significance of the events of the Exodus as being for people living after Jesus, because he sees them as being fulfilled in Christ. That of course clashes with the conventional view (in many circles) of how to understand the Bible. The main significance of the passage is found in Jesus and for those who seek to follow him. It doesn't bother Paul that it was originally written 1000 years before the events that give it its main meaning.
Peter also agrees that the main significance of passages in the Old Testament wasn't understood until Jesus. Furthermore, he even argues that the writers knew that they didn't fully understand.
Concerning this salvation, the prophets who prophesied about the grace that was to be yours searched and inquired carefully, inquiring what person or time the Spirit of Christ in them was indicating when he predicted the sufferings of Christ and the subsequent glories. It was revealed to them that they were serving not themselves but you, in the things that have now been announced to you through those who preached the good news to you by the Holy Spirit sent from heaven, things into which angels long to look.
1 Peter 2:10-12, ESV
I therefore conclude that the main significance of a Bible passage is the one that takes into account the original context and significance, but which points through them to Jesus. To my mind, if an Old Testament commentary doesn't do that, it is missing the main point.