It is clear that passions, feelings, or emotions can be good or bad. First of all some are in themselves pleasant (and in this sense good), such as joy, hope, and similar emotions, others in themselves unpleasant (and in this sense bad), such as sadness, anxiety, and the like (though they can be good with respect to their purpose, as will shortly be evident). Secondly, and more importantly, passions can lead us to good actions or away from harmful actions. Fear of one's child being harmed may lead a person to give greater attention to the child; hope of completing a great project may lead a person to persevere and to give greater effort, and so on.
Thus the passions can be good and useful (or harmful, as the case may be), and in this sense have relevance for a human and moral life. But do the passions themselves have moral value? Are they themselves morally good or bad?
It might seem that passions are not morally good or bad, since they are, after all, passive. They aren't something we do, but something we feel. Thus they don't seem to be voluntary, to be something we are responsible for, and so we can neither be blamed nor praised for them.
But this objection doesn't sufficiently take into account the various indirect ways in which we can control our feelings, and thus ways in which feelings themselves are voluntary, though indirectly. A person is able to, for example, nourish a grudge, by deliberately thinking about his grievance against someone. Similarly someone is able to increase feelings of sympathy, inasmuch as, e.g., he imagines himself in the place of a suffering person. Or again, to decrease his anger, inasmuch as he takes care to think on the bigger picture, on positive aspects of the situation instead of negative ones, etc. In such cases the greater or lesser degree of emotion is itself voluntary, to the extent that one voluntarily promotes or hinders it.
A lesser, but still very important way in which an emotion or lack thereof can be voluntary, is inasmuch as someone is physically, psychically and morally capable of doing something to increase or lessen the emotion, and ought to do so, yet fails to do so. In this case the omission itself, being voluntary, makes the consequent lack of influence over the emotion also voluntary in a secondary way. Thus a person inclined to violent anger, if he fails to take any precautions to control his anger, may be rightly blamed for the escalation of his anger.