A number of pastoral encounters recently have prompted me to write something regarding the whole issue of anger, as many people (I have learned) really struggle with feelings of anger and wonder about it.
In my pastoral (and personal) experience, anger is an emotional reaction direction against some sort of "wrongness". It can be because something that is present in a given situation really should not be there, or because something that isn't present should be. Either way, we detect, on what is often a non-rational level, the presence of this wrongness, and anger is the result. It isn't always expressed outward, mind you — that is anger-as-power — but it is real.
Now some people wonder if anger is a sin. It depends: Jesus, as we know, got angry sometimes. What makes the difference is if the anger being felt is in accordance with right reason. Does the "wrongness" we are detecting actually exist? And will getting angry be of any positive use? For anger to be "righteous", both conditions must be fulfilled. Righteous anger, then, actually flows out from a personality imbued with the gift of wisdom. Of course, this gift is not strong in everyone, so while there are some whose anger is habitually righteous, those for whom this gift is not strong are advised to instead regularly take the often-given advice of the Scriptures to keep their mouths shut.
Sinful anger, also known as wrath, is known particularly by its opposition to justice and forgiveness. Wrath is also a response to a "wrongness", but it is a response that is inappropriate in some way. It might be displaced in time, for example: the wrongness happens now, but the anger response comes so much later that there is no real obvious connection except in the vengeful heart of the person detecting the wrongness. Or perhaps the reason the anger is really wrath is because the response is disproportionate to the wrongness: shooting someone out of road rage is clearly disproportionate to the "wrongness" of lousy driving or bad traffic. Wrath is particularly bad when the real "wrongness" being addressed is some character flaw in the angry person: some people only feel alive when mad, and so they look for excuses to get mad so that they can seem to be addressing one wrongness but really are only addressing the "wrongness" of their own dead heart. Wrath, in its worst form, is a direct extension of the sin of pride: like Adam the person "wants to be like God", but isn't, and so turns to habitual anger in order to feel powerful. What makes it truly diabolical is that it creates and feeds the "wrongness" situations that then feed the anger. It is the wrath of tyrants, and of Satan himself.
Now some people are disturbed when they feel angry because they find themselves getting angry about something that never disturbed them before. It is possible that this is a form of moral backsliding, but it is also possible that what is really occurring is that the mind is becoming more precisely tuned to identify the objective existence of "wrongness". An abused child often feels sad more than angry, because the child does not yet realise that it is "not his fault". Once this realisation is made, however, anger often surfaces, and it is not necessarily inappropriate, as (once again) it is a reaction to a situation whose "wrongness" is only now just recently discovered. This kind anger is often the source of great pain, because the motive to correct the "wrongness" may not have an object anymore. At least, however, it is possible to reassure people that the anger is not, in and of itself, necessarily inappropriate.
The simple reality is that anger comes to us, but it isn't always useful. We need to be guided by renewing of our minds and hearts so that, when anger does come, the energy that it brings can be put to positive (rather than destructive or self-destructive) uses. The key is to develop a spirit of forgiveness. The ability to readily and truly forgive the debts owed to us, particularly emotional debts, lets the non-righteous anger roll off us like water off a duck's back. And anger that does remain is then like the righteous wrath of God, which will be manifested on the Last Day when Jesus comes in glory to purge the world of diabolical evil/wrongness. May we all develop hearts like those of the heart of God, whose initial instinct is compassion and mercy.