"...the anger of man does not achieve the righteousness of God."
~James 1:20
I read this verse a few weeks ago and have meditated on it a bit since then.
In the book of Ephesians, Paul advises us to "be angry, and yet do not sin" (4:26). He knew that as humans, anger is an inevitable emotion for all of us in this fallen world. But he also knew that without the love of God in our hearts, this anger can become a catalyst in the manifestation of any number of sins since without His help, we have no hope of controlling this powerful emotion on our own.
Being angry on occasion is normal, and sometimes even beneficial if we keep tabs on it and deal with it properly. But we're not designed to harbor our anger continuously. That's where the above verse in James comes in. Even if we call on God's help in the midst of an episode of anger, and we are successful in avoiding any kind of sin during that time, I really think being angry for an extended period of time can prevent us from running after His righteousness and blessings. Of course there are exceptions to this rule; sometimes righteous indignation combined with Providence can certainly further God's kingdom (such as Jesus turning over the money-changers' tables in the Temple). But for the most part, we're better off if we deal with our anger quickly and concisely, without giving in to the temptation to sin and without letting our anger keep us from doing what God has called us to do.
I'm usually not one to act out on my anger; I tend to be more prone to stuffing my anger inside and letting it stew instead. But I'm thinking that doing this is really just as bad as physically acting out my anger. If I'm angry at someone, and do nothing to fix the situation, I'm usually rendered useless in regards to His kingdom. In addition, that anger makes me vulnerable toward more attacks from the Enemy; just check out a later verse in that passage in James, where he says that allowing our anger to remain in us only gives the devil "an opportunity" (v. 27), or in other translations, "a foothold." Anger will only beget more anger, and that anger will only beget sin, unless we call on God the minute that powerful emotion sets in and ask for His help in resolving it. A life bent toward achieving His righteousness can't be spent wading in the mucky waters of anger and bitterness.