... anger is often linked with another passion—pride. Now we will go so far as to say that anger does not often appear as an independent or fundamental passion in the human heart. Most often anger expresses the dissatisfaction of another passion, or even of the casual desires that a person may have from time to time. In the latter case, anger is called impatience or obstinacy, which in turn are expressions of a general self-love, lack of brotherly love and lack of desire to attend to oneself and struggle with oneself. The stronger a passion is in a person, the quicker and more fiercely it turns into anger when it is not satisfied. Thus the vainglorious and lovers of money become envious, the lustful become jealous, the gluttonous become over-critical and irritable, and so on. In general, anger is an indication of various sinful passions, and one can find out about these by noticing when a person begins to get angry: if it is during a conversation about fasting and sobriety, then he sins with the passion of overeating and drunkenness; if it is on occasions when he loses money—love of money; if during talks about the saints' feats of humility—he is proud, and so on. This is why we began our instructions to spiritual fathers with the struggle against anger, as it is an involuntary indicator of other passions. A person's enslavement to them is expressed first of all as enslavement to anger, which bursts out even with very cunning people who are otherwise able to hide their passions and keep quiet about their bad habits.
Metropolitan Anthony (Khrapovitsky), Confession: A Series of Lectures on the Mystery of Repentance, trans. Fr. Christopher Birchall (Jordanville, NY: Holy Trinity Monastery, 1996), 53.