Thanks for this very important question. As you’ve pointed out already, context is often the determining factor when dealing with Bible difficulties or apparent contradictions. As you’ve found, it’s usually the case that a fuller reading of any passage of scripture usually clears up the issue quickly.
A good friend of mine, Greg Koukl, has a wonderful little handout cleverly called “Never Read a Bible Verse” that addresses methods by which we can better understand Scripture and deal with such apparent contradictions. Basically, he says that reading a single Bible verse can sometimes lead to misunderstanding because the Bible has a rich and often broad context that illuminates the meaning of a particular verse in light of the whole of Scripture. Here is the link.
In a nutshell, Greg (and I) would offer this advice:
The immediate context of a verse will often solve the issue. There are times, however, when the immediate context of the text doesn’t do the trick. There’s no need to despair, however. Usually, the broader context solves the issue. In other words, the immediate context of the surrounding verses should be read, then the surrounding paragraphs and event chapter of the book, then the whole book itself, and then the entirety of the Bible. Understanding why a particular book of the Bible was written (Kings and Chronicles were meant to outline the stories of the Israel’s monarchy, etc., while prophetic books like Isaiah, Ezra, Ezekiel and Micah were full of symbolism, warnings, and eventual hope). The prophetic books contain facts and truth claims, but some of what they convey isn’t meant to be taken woodenly. Rather, they are meant to be symbolic or even merely convey the heart of God as to a particular situation involving a particular people for a particular time.
Also, there is a cultural context to take into consideration. The Bible was written in three languages (Hebrew, Aramaic, and Greek) in ancient times. Thus, for it to make sense to the audiences, it had to employ the communication customs of the day. One of those customs includes hyperbole (and in the Middle East, hyperbolic language is quite alive and common). This entails using broad statements (like “never” and “always”) to convey ideas rather than precision.
So let’s look, for example, at the two verses you specifically mentioned.
In Michael 7:18, the Bible says “Who is a God like you, pardoning iniquity and passing over transgression for the remnant of his inheritance? Doe does not regain his anger forever, because he delights in steadfast love.” The next verse talks about God again having compassion and casting sins away. Why? Because Micah as a book is divided into two messages: (1) God’s judgment for iniquities of the unrepentant and those who reject God and (2) God’s compassion on those who look to God for their salvation instead of themselves (Micah 7:1ff tells us this).
Now, let’s look at the context of Jeremiah 17:4, which says “for in my anger a fire is kindled that shall burn forever” (ESV). Other translations are similar in saying that a fire is kindled in God’s anger. The NIV has it that “You have kindled my anger, and it will burn forever.” Looking at the Hebrew, I think the other translations are more literal. This is important because they don’t say that God’s anger burns forever, but the fire that is kindled in God’s anger burns forever. This could easily mean his righteous judgment for the unrepentant sins. If that is true, then there is not contradiction because Micah says God’s anger doesn’t last forever and Jeremiah says that the fire kindled in his anger does.
But the best understanding is given to us in the opening verses of Jeremiah 17. There we read that the sins of the kingdom of Judah are “written with a pen of iron, with a point of a diamond it is engraved on the tablet of their heart…” What this indicates is that the rebellious sinners of Judah are unrepentant and their desire to reject God is unchanging. It is against such people that God’s anger would last forever. But then the next few verses say that “Blessed is teh man who trusts in teh Lord, who trust is the Lord. He is like a tree planted by water, that sends out its roots by teh stream and does not fear when heat comes…” (Jer. 17:8). How poetic! What this is saying is that those who trust in God (not themselves) will not burn in the fire kindled in his anger! Jeremiahs says “O Lord, the hope of Israel, all who forsake you shall be put to shame…for they have forsaken the Lord, the fountain of living water” (v. 13). In other words, God’s fiery anger will last forever for those who reject the living water that saves them from being scorched. But those who trust in God will be watered and shall not be scorched.
Thus, there is no contradiction. Micah specifically says that God’s anger doesn’t last forever for those seeking his salvation and redemption. Jeremiah says exactly the same thing.
This technique almost always clears up the apparent contradictions. But let me say this in closing. It is very easy to lodge objections and make things seem contradictory. Frankly, anyone can do that. It takes care and thought to lodge a legitimate objection, just as it takes care and thought to respond. My advice is this: whenever you see cleverly phrased objections that seem to destroy a worldview in just a few minutes, the chances are high that the person lobbing those objections doesn’t really understand the worldview he’s critiquing.
Hope that helps!