One of my favorite features of Scripture is the internal commentary. I love the parts that comment on other (usually earlier) passages. Sometimes those commentaries add a bit of color to the earlier passages. Sometimes they seem to change the whole story.
Deuteronomy is a good example. Moses' commentary on the events from Exodus through Numbers adds nuance on some places, clarifies what the take-home message is in others, and sometimes seems to change the entire story.
For example, Numbers 13:1–16 tells us about the spies that Moses sends into the land from Kadesh-barnea. In the Numbers account, the Lord commands Moses to send the spies into the land. But Deuteronomy 1:22–25 tells us that sending the spies was the people's idea, and Moses agreed to it. In light of the commentary in Deuteronomy, it seems like the Lord's command in Numbers 13 was not to choose spies, but to send them into the land.
Another example might be Deuteronomy 10:1–5. Here Moses tells us about receiving the second set of tablets at Sinai, which is also told in Exodus 34:1–9. In both accounts, Moses is to bring stone tablets up the mountain; but in the account in Deuteronomy, he was told to build an ark for them first. I suppose that could be the Ark of the Covenant, but the description in Deuteronomy suggests it was something else. As far as I know, only Deuteronomy 10 mentions this ark.
We might also mention the relationships between 1 and 2 Kings and 1 and 2 Chronicles. There are several accounts in 1 and 2 Kings that read very differently in light of the accounts in Chronicles. As an example, the story of Manasseh in 2 Kings 21:1–18 reads very differently than the same story in 2 Chronicles 33:1–20. It seems from both books that Manasseh is the worst king Judah had (2 Kings 24:3, 2 Chronicles 33:9, Jeremiah 15:1–4). But the account in 2 Chronicles tells us that Manasseh repented, the account in 2 Kings doesn't mention that.
As an aside, Manasseh's reign was the longest of any king of either Israel or Judah: 55 years (1 Kings 21:1). I think it's significant that the Lord allows the worst king to reign the longest, eventually bringing him to repentance. There are hints of Romans 2:4 in that.
Our favorite passage is Romans 4:1–8. Notice how that seems to turn the Old Testament on its head: Abraham is God's friend (James 2:23), but it's not because he was a particularly good person. Abraham was God's friend because he believed what God said.
Or we might notice how Romans 3:20 sums up the entire Old Testament in one sentence: "by law comes the knowledge of sin." We'll follow J. N. Darby here to point out that it's "sin," not "sins." Romans isn't claiming that the Mosaic Law told us that specific acts are sins, as though we hadn't already known. Rather, it reveals to us our own indwelling sin. It demonstrates that fallen men and women are incapable of submitting to God. And we might notice that Moses' commentary of the exodus says the same thing (Deuteronomy 29:4).
Romans 9:6ff is another commentary on Scripture that turns the Old Testament accounts on their heads. We might read about Isaac and Ishmael (Romans 9:7ff), Jacob and Esau (Romans 9:11ff), or the children of Israel at Sinai (Romans 9:15-16) from the Pentatuech and not see what the Spirit of God brings out in Romans. But if we take Romans 9 to heart and look back at those stories, they read very differently.
I've probably read too much Darby, but I really think Romans 9:15–16 (quoting Exodus 33:19) is the crux of Christianity. God can either condemn us, or He can "hide in His sovereignty" and show us grace. There's not a third option. God would be entirely righteous simply to condemn us all. In fact, His righteous nature would drive Him to do exactly that. He can only act in grace towards us – any of us – by claiming His right to sovereignty as our Creator.
Now, I really don't like using words like "sovereignty" because Scripture does not. Or at least, it doesn't use it much, I guess we might claim 1 Timothy 6:15 (NASB) as justification. But in the end, the idea is there, even if the word isn't. "I will have mercy upon whom I have mercy" shows exactly on what ground God can show mercy to us.
And that ties into our earlier thoughts about Manasseh and his 55-year reign. God chose to have mercy on Manasseh and He did. He gave the worst king the longest time to repent.
That's worth mulling over.