As Christians, we are to ensure our anger is righteous.
How do we do this?
The word we see for anger in Ephesians verse 6 is Greek – or-gid’-zo. It is not an unbridled rage or anything of the sort but indicates a particular form of anger. It is “a deep-seated, determined and settled conviction.” Such an anger could be sinful but it is highly dependent on the motive behind it. As such, it could just as easily be a justified anger.
In Ps. 4:4 we see David say “Be angry, and do not sin…” So, if we are commanded to be angry and yet not fall into error, that would mean that there must be a way to be angry in a good way.
What Paul is referring to in Ephesians is what would be described as a righteous indignation. We are called to hate sin, hate evil, hate injustice, etc.
So, what particularly makes anger bad?
Anger that is self-defensive, self-serving, or resentful is sinful. It is sinful when God’s goal in a matter is distorted by such things. Anger is also sinful when it is allowed to linger (when you refuse to let it go and continue to stew on it). It is also sinful when you attack the person rather than the problem (the old adage, hate the sin, not the sinner sort of thing).
Interested in a little more?
Start here: http://www.faithbaptistorlando.com/resources/sermon/2017-03-19/throwing-off-the-conduct-of-our-old-life