"But I say unto you, That whosoever is angry with his brother without a cause shall be in danger of the judgment . . ." (Matthew 5:22).
There are a number of Scriptures which, taken alone, would indicate that a Christian should never get angry about anything. For example, note Ephesians 4:31: "Let all bitterness, and wrath, and anger . . . be put away from you. . . ."
Yet Jesus indicated only that anger "without a cause" was wrong and invited judgment. Many modern translations omit the phrase "without a cause" in this verse (NIV, NASB, LB, TEV, etc.), but the phrase does occur in over 99.5% of all the Greek manuscripts, and thus clearly should be retained.
If anger were never permitted for a believer, it would contradict even the occasional example of Jesus Himself. "And when He had looked round about on them with anger, being grieved for the hardness of their hearts . . ." (Mark 3:5). He was angered here by certain hypocrites among the Pharisees who were ready to condemn Him for healing a disabled man on the Sabbath.
We are never justified in getting angry over some personal injury or insult to ourselves. This is implied in context in such verses as cited above (Colossians 3:8, etc.) "Recompense to no man evil for evil . . . avenge not yourselves, but rather give place unto wrath" (Romans 12:17,19). But if we do get angry in spite of ourselves, we are commanded: "Be ye angry, and sin not: let not the sun go down upon your wrath" (Ephesians 4:26).
There may be some situations involving injury or insult to the name or work of Christ where anger is indeed "with cause." Even then, however, God would warn us to be "swift to hear, slow to speak, slow to wrath" (James 1:19), remembering that "Vengeance is mine; I will repay, saith the Lord" (Romans 12:19). HMM