Is Anger a Sin?

ANXIETY of mind (Anger) is the mental grief we feel due to our involuntary ailments. Whether the evil is exterior like poverty and illness or interior, such as lack of knowledge, dryness, depression or temptation. Then we at once begin to try to eliminate it, and find a way to shake it off. For it is natural to us all to desire good, and take off that which we take to be evil.
If any one wishes to be delivered from his troubles out of love of God, he will strive patiently, gently, humbly and calmly, looking for deliverance rather to God’s Goodness and Providence than to his own efforts. However, if self-love is the prevailing object, he can grow hot and eager in seeking relief as though all depended more upon himself than upon God. I do not say that the person thinks so, but he acts eagerly as though he actually think so. Then if he does not realize what he desires at once, he becomes extremely impatient and troubled, which does not settle matters, but on the contrary makes them worse. And so he goes into an unjust state of anxiety and distress, till he begins to see that there is no cure for his trouble. By then, you would see how a disturbance, which was right at the offset, begets anger, and anger goes on into an excessive distress, which is exceedingly bad.
Anger is the highest evil which can happen to the soul, which is a sin solely excepted. Just as internal commotions and seditions ruin a commonwealth, and create it incapable of resisting its enemies, so if our heart be troubled and anxious, it loses power to hold unto such graces as it has, as well as the energy to resist the temptations of the Evil One, who is all the more eager to fish (according to an old proverb) in troubled waters.
Anxiety arises from an unregulated want, to be delivered from any pressing evil. Birds that are caught in nets and snares become inextricably entangled inside the cage, because they flutter and struggle a lot. Therefore, whenever you desperately want to be delivered from any evil, or to get a hold of some good thing, attempt above all things to keep a calm and a restful spirit, steady your judgment and will, then go quietly and simply after your object, taking all necessary means to achieve that.
When I say “simply” I do not mean carelessly, but without keenness, uneasiness or anxiety.
Examine yourself daily , at least night and morning, as to know whether your soul is at peace or whether it has been twisted thence by any passionate or anxious emotion. See whether your soul is totally under control, or whether it has run into some unruly love, hate, envy, lust, fear, vexation or joy. And if it has gone a strayed, before everything else look out for it and quietly bring it back to the Presence of God, and again placing all your hopes and love under the direction of His Holy Will. Just as one who is scared to lose some precious possession holds it tight in his hand, so, like King David, we ought to be able to say, “My soul is always in my hand, and therefore I have not forgotten Thy law”.
Do not give way to any desires to disturb your mind under the pretext of their being trifling and unimportant; for if they have their way that day, higher and heavier matters will find your heart more accessible to disturbance. When you are acutely aware that you are growing anxious, put in yourself to God, and decide deeply not to take any steps whatever to obtain the result you desire, until your disturbed state of mind is totally in peace.
If you will be able to lay your anxiety before your spiritual director or at least before some trusty and faithful friend, you may be sure that you will find greater peace. The heart finds relief in trusting its troubles to another, just as the body when suffering from constant fever finds relief from bleeding.