After lies (Ephesians 4:25), anger should be next on the Christian's hit list of 'old ways to be dealt with'.  Anger is sometimes a difficult issue to think about.  It is not always wrong, because we know that God is angry against sin and rebellion (Nahum 1:2).  That is why Jesus came to suffer the punishment of the cross, so that we might be uncoupled from God's wrath (1 Thessalonians 5:9).  Righteous anger is God's anger against sin and rebellion (Romans 1:18).  There are times when Christians can properly be angry against injustice.  But our old sinful nature rarely gets anger on target. The goal posts move rapidly from anger against the offence to hatred against the person ... and that causes problems (James 1:19-20).

Of course the devil wants to create as many problems as possible. And the overspill from righteous anger suits his purpose splendidly. It instantly turns a rightful concern into an unrighteous vilification, and godliness is overturned.  Anger may have a short or long fuse, but once it starts to ignite and take hold it is very difficult to stop it before it damages relationships and sometimes physical property or people.  It is important to understand that anger is not just a psychological phenomenon, or easily inflamed by adrenalin.  It also can be a demonic tool.  It led to Abel's death (Genesis 4:6-8) and Jesus' death (Luke 6:11), it persecutes the church (Acts 7:54-8:3), it solves nothing and tears churches apart from the inside: instead the godly response is to pray (1 Timothy 2:8).     

An old surgeon was preparing young doctors for their surgical exams, and he misquoted this verse as, "Let not the sun go down upon un-drained septic pus".  He wanted to impress the point that sepsis (particularly in the pre-antibiotic era) was potentially fatal if left unattended overnight.  In the same way, (changing the metaphor), anger allowed to fester can be as dangerous as an unexploded bomb in the back garden.  It can lie dormant for years, but an appropriate trigger will release the full explosive power to injure many.  An essential spiritual discipline for every believer is to commit every injustice to the Lord before we sleep and hand over responsibility for that injustice to Him.  Romans 12:19-21 says, "Do not take revenge, my dear friends, but leave room for God's wrath, for it is written: 'It is mine to avenge; I will repay,' says the Lord. On the contrary: 'If your enemy is hungry, feed him; if he is thirsty, give him something to drink.  In doing this, you will heap burning coals on his head.'  Do not be overcome by evil, but overcome evil with good."

Most of us like to think we are reasonable and tolerant. But the stress of pressurised business, professional, family or church life can bring out the worst in us.  That is why it is well worthwhile to think ahead.  Anger that seeps into the night is neither objective nor righteous.  There may well be an issue to deal with - so deal with it.  Or there may be an injustice to forgive - so do it.  It may be that the injustice continues and it is not in your hands to punish or vindicate - leave that to God (Hebrews 10:30).  He may ask us to work with Him in the matter but obedience will be the motive rather than uncontrolled anger.  The family, church and working environments give plenty of scope to put all this into practice - before bedtime!