What is a passion? They are impulses that move us to action by overcoming our will. Because of this we say they enslave us. They are powerful because they are also desires which cannot be satisfied. They act as a force that goes against what we know to be the proper action and lead us to actions which are counter to the commandments of Christ. There is no single list of these passions, but the following is a common list used in early Christian literature: gluttony, unchastity, avarice, anger, dejection, listlessness, self-esteem and pride.
Their ultimate cause is the forgetting of God. Healing begins with faith.
Not all passions are bad. There are both natural and unnatural passions. Our natural passions are our appetite for food, enjoyment of food, fear and sadness. These are necessary for our the preservation of our nature. They are important animal aspect of our being given to by God. But we are more than animals as we are spiritual. Because of this we have an aspiration for the infinite. Often these natural passions which are intended for earthly preservation are transformed into unnatural passions. They are frequently transformed into a mistaken quest for the infinite in things of this material world. The soul loses control and the passions take over. Out task is to control them so they can be limited to their proper purpose. Then they can channeled to seek divine things.
Saint Maximus says,
The natural passions become good in those who struggle when, wisely unfastening them from the things of the flesh, use them to gain heavenly things. For example they can change appetite into the movement of a spiritual longing for divine things; pleasure into pure joy for the cooperation of the mind with divine gifts; fear into care to evade future misfortune due to sin and sadness into corrective repentance for present evil. So the natural passions are not necessarily bad. When we are thinking of God they are kept to their necessary biological functions. Our task is not to eradicate them but to control them, keeping them within the limits necessary for the preservation of the body. They must continually be watched and controlled. This is the basis of asceticism.
Thoughts from Fr. Dimitru Staniloae:
Asceticism means, in the spirit of Eastern thought, the restraint and discipline of the biological, not a battle for its extermination. On the contrary, asceticism means the sublimation of this element of bodily affectivity, not its abolition.... Natural passions can assume a spiritual character and give an increased accent to our love for God.... Now here is the most important point. By controlling them we increase our spiritual blessings.
Fr. Dimitru says,
By putting a bridle and a limit on the pleasure of material things, a transfer of this energy of our nature takes place, in favor of the spirit; pleasure in spiritual blessings grows. ... The challenge we face is not easy. Is difficulty is increased by our tendency to react in the wrong way. Once a pleasure leaves us we feel a loss. This can be painful. Pain or dissatisfaction always follows pleasure. This pain that follows does not lead us to take action to temper the pleasure, but does the opposite. We seek even more pleasure. The cycle continues without satisfaction.
Fr. Dimitru says,
The pain which follows pleasure, instead of making him avoid pleasure, as its source,...pushes his anew into pleasure as if to get rid of it, tangling him even more in this vicious chain. Asceticism is aimed at breaking this dysfunctional cycle of pleasure and pain, liberating us from the unnatural extension of passions that have a proper role in our bodily preservation. This bodily domination through uncontrolled passions is our main block to union with God.
Reference: Orthodox Spirituality, pp77 - 89