Freedom from anger is an important divine quality mentioned in the Bhagavad Gita (16.2).
Anger is a negative and harmful quality that leads to spiritual ruin. Therefore it is important that spiritual aspirants avoid anger. According to the Bhagavad Gita (2.63), anger leads successively to the following: delusion, loss of memory, loss of discrimination, and spiritual ruin.
Sattva (purity and calmness), rajas (desire and passionate activity), and tamas (dullness) are the three qualities that constitute physical and mental nature. Tamas means the darkness of ignorance. It breeds delusion. Delusion clouds our perception and perverts our understanding: we mistake wrong for right, bad for good, immoral for moral, and so on. As a result, we lose memory of all the positive things we have learnt since our childhood. We forget that as responsible members of society we have to act in a mature and rational way. We forget the scriptural teaching that we are not just body and mind, but essentially divine. Loss of this memory leads to loss of discrimination, the only faculty that differentiates human beings from animals. When discrimination is lost, it leads to spiritual death. We just live as social animals and miss the goal of life, which is the manifestation of the divinity inherent in us.
Sri Krishna teaches Arjuna that desire and anger compel people to commit sin in spite of themselves, as if driven by force. These two qualities spring from rajas. (Bhagavad Gita, 3.36) Though we need rajas to overcome tamas and ascend to sattva, we should avoid its negative aspects: desire, anger, anxiety, fear, and attachment.
Discrimination, reflection, prayer, and repetition of the divine name are means to avoid anger and be steadfast in our spiritual quest. Says Swami Turiyananda, a disciple of Sri Ramakrishna: "Anger is a concentrated form of lust. It makes one lose one's head completely. Lust does not so absolutely overwhelm the mind....With the gradual increase of love of God, lust, anger, etc. wane out."