trividham narakasyedam dvaaram naashanamaatmanaha |
kaamaha krodhastathaa lobhastasmaadetattrayam tyajet || 21 ||

Three gates of hell cause one’s destruction, desire, anger and greed. Therefore, give up these three.
trividham : three
narakasya : hell
idam : these
dvaaram : gates
naashanam : destructive
aatmanaha : oneself
kaamaha : desire
krodhaha : anger
tathaa : and
lobhaha : greed
tasmaat : therefore
etat : these
trayam : three
tyajet : give up
Like a good teacher, Shri Krishna summarizes the entire chapter comprising the rather lengthy list of devilish qualities into three main ones: desire, anger and greed. He says that we always need to watch out for these three qualities in our daily lives, and minimize them as much as possible. He calls them gateways into hell, because they lead to the path of destruction rather than the path of liberation. Even the order of these three is important, because both anger and greed follow desire.
The second chapter explained how kaama or desire comes into our lives. Dhyavato vishayaan, by constantly thinking of an object (or a person or a situation), we develop an association with it. If carried on for long, this association results in a desire to procure that object. If anyone or anything comes between us and the object, we develop anger. And once we have the object, once our desire is fulfilled, we want more of the object. This results in greed.
So then, how do we tackle these three gates of hell? Let us first look at kaama or desire. If desire develops through contemplation of objects, we can reduce desire to a certain extent by keeping a watch on what we expose our mind to. For example, we can go to the mall with a shopping list rather than wander around shops that we don’t need anything from. But the root of desire is the labelling of objects as desirable by our mind. This labelling or superimposition is known as “shobhana adhyaasa”. It is why the same dress looks desirable to one person and irrelevant to another, since objects by themselves are not desirable. Controlling and convincing the mind through study of scriptures and meditation helps to reduce this labelling.
Desire is somewhat easy to control, but once we are in the grip of anger, it becomes somewhat difficult to do so. At least we do not publicly display our desires, but we do not hesitate to show our anger publicly. We require tremendous control over our mind in order to release ourselves from the grip of anger. It is therefore better to focus on rooting out unnecessary desires than to confront anger directly.
Lastly, lobha or greed can be kept in check through charity. Anytime we start feeling pride over our wealth or possessions, we should immediately donate a portion of our wealth or possessions. How exactly we should do so is covered in the next chapter.