Paul realized the potential for devastating harm that can come from unbridled rage. That is his reason for giving three qualifying prohibitions that follow this call to be angry. Don't sin . The command is not to avoid anger, but to avoid sinful anger. If we don't keep antagonistic emotions on a tight leash, they will cease to be useful in restraining sin, and instead will begin to multiply it.
Bitterness siphons off passion for life.
It displaces faith and love. Don't nurse anger . Don't stuff it inside and brood over it. It will only fester. Take it out of the dark and expose it to the light.