Today's passage has an interesting little verse. Here's what verse 26 (and 27) says in the ESV: "Be angry and do not sin; do not let the sun go down on your anger, and give no opportunity to the devil." What's going on with this verse? Is it telling us to be angry? How can we be angry and not sin? Isn't anger a sin? It's a pretty short thought, but leaves a lot of questions in my mind.
Luckily, the very wise and pastoral Biblical Greek scholar Bill Mounce has done a few posts on this topic. It can get technical at some points, so I'll summarize his thoughts for you. First, his introduction:
"I have been thinking about anger lately. I was raised in a traditional Christian home and church, and like many people believed that anger was wrong. Period. Anger was the response of people who who weren’t mature in their faith and had not experienced the sanctifying work of the Holy Spirit. I don’t remember being taught this explicitly, but I suspect it was part of our cultural environment.
This is why Eph 4:26-27 always bothered me. In the NIV it says, “‘In your anger do not sin’: Do not let the sun go down while you are still angry, and do not give the devil a foothold.”
...Forget the fact that it is impossible to release all anger and forgive all offenses (completely) within a 24 hour period. If someone says they able to do this, I suspect they are a very legalistic, religious person. Deep offenses, even for the highly mature, take time to forgive and for anger to dissipate. Only one person I know was able to forgive all offenses immediately, and he was hanging on a cross the last time he had to do so." 
He goes on to struggle with the Greek verb for "anger" and whether or not in this passage it is an indicative (saying "If you happen to get angry", simply making a statement about it) or an imperative (a command, "Be angry"). Different translations really struggle with how best to understand this phrase. He goes on to write:
"The other thing that bothered me was when a counselor friend of mine said that anger was an emotion and as such was not intrinsically evil. “Emotions,” he said, “are not good or bad, right or wrong. It is an issue of what you do with them.” I didn’t believe him at first (since I was such a “good Christian”; see my earlier comment), but I did know that anger is the just and right reaction of God to evil, but of course we just called that the “wrath of God” (cf. Heb 3:10, 17) and didn’t make any application to human life.
But to make it even more complicated, James writes, “Everyone should be quick to listen, slow to speak and slow to become angry” (1:19). Wait a minute. Are we called to become angry, and then be sure it dissipates by nightfall, or are we to become angry slowly?" 
So what conclusion does he come to?
"ὀργίζεσθε is, I think, clearly an imperative...We are told to get angry. The other side of the coin, and a necessary side — have you ever seen a coin with only one side? — is that anger is to be balanced with not sinning.
How do you not sin? “Do not let the sun go down while you are still angry, and do not give the devil a foothold” (v 27, NIV). We don’t allow the anger to move to sin by not giving it a sustained presence in our life; we deal with the situation that has caused us anger, by sunset. And when we do this, we are not letting Satan have a toehold in our life. To continue to live in anger is, in fact, giving Satan a toehold in our life, and he will most certainly use that position to launch a full offensive into our heart." 
Mounce continues on, analyzing what the NT has to say on this issue of anger. I won't post it all here - you can read all of it if you click the links at the bottom - but make sure you read this next part, because it is a very important explanation:
"There are some situations in which anger is the right and only response, but the limitations the context places on the imperative is what keeps the response measured and appropriate. I have often wondered if Jesus was angry. We think of the cleaning of the temple, but the text never says he was angry. In fact, the only time that [anger] is used of Jesus is in Mark 3:5 where it describes his response to the Pharisees’ desire to catch him healing on the sabbath. “He looked around at them in anger and, deeply distressed at their stubborn hearts, said to the man, “Stretch out your hand” (NIV). Now interestingly, [deeply distressed] means, “be grieved with, feel sympathy”. Interesting; Jesus holds anger and sympathy hand-in-hand. Maybe there is a clue here to our theology of anger...
...Yet another clue is the admonition in the New Testament that believers not to be given to anger (Eph. 4:31; Col. 3:8; 1 Tim. 2:8). So another helpful verse supporting the imperative of Eph 4:26 is Jam 1:19; “Understand this, my dear brothers: everyone must be quick to listen, slow to speak, and slow to become angry” (ESV). We are to become angry slowly, and relinquish it quickly.
There is much more that could be said, but this is enough to convince me that the imperative in Eph 4:26 means what is says. Hoehner has this to say, and it is helpful. “When God is angry, he is always in control of his anger. Unlike God, however, people have a tendency to allow anger to control them…. A believer who is controlled by the Spirit is angry at the right time and never angry at the wrong time. For example, when someone in the body of believers has been wronged, it is correct for one to be angry but not to be consumed by that anger” (page 621)...
...The fact of the matter is that when faced with evil, it should illicit anger. It did for Jesus. It does for God. We will see it in all its fury at judgment. But as Hoehner says, it must be at the right time in the right way, with anger never controlling us."  (emphasis mine)
Very, very important thoughts for today. Questions or comments on any of it?