Commentary by His Holiness the Dalai Lama
This verse really gets to the heart of what could be called the essence of the practice of the buddhadharma. When we talk about Dharma in the context of Buddhist teachings, we are talking about nirvana, or freedom from suffering. Freedom from suffering, nirvana, or cessation is the true Dharma. There are many levels of cessation--for example, restraint from killing or murder could be a form of Dharma. But this cannot be called Buddhist Dharma specifically because restraint from killing is something that even someone who is nonreligious can adopt as a result of following the law. The essence of the Dharma in the Buddhist tradition is that state of freedom from suffering and defilements (Skt. klesha, Tib. nyonmong) that lie at the root of suffering. This verse addresses how to combat these defilements or afflictive emotions and thoughts. One could say that for a Buddhist practitioner, the real enemy is this enemy within--these mental and emotional defilements. It is these emotional and mental afflictions that give rise to pain and suffering.
The real task of a buddhadharma practitioner is to defeat this inner enemy. Since applying antidotes to these mental and emotional defilements lies at the heart of the Dharma practice and is in some sense its foundation, the third verse suggests that it is very important to cultivate mindfulness right from the beginning. Otherwise, if you let negative emotions and thoughts arise inside you without any sense of restraint, without any mindfulness of their negativity, then in a sense you are giving them free reign. They can then develop to the point where there is simply no way to counter them. However, if you develop mindfulness of their negativity, then when they occur, you will be able to stamp them out as soon as they arise. You will not give them the opportunity or the space to develop into full-blown negative emotional thoughts. The way in which this third verse suggests we apply an antidote is, I think, at the level of the manifested and felt experience of emotion. Instead of getting at the root of emotion in general, what is being suggested is the application of antidotes that are appropriate to specific negative emotions and thoughts.
For example, to counter anger, you should cultivate love and compassion. To counter strong attachment to an object, you should cultivate thoughts about the impurity of that object, its undesirable nature, and so on. To counter one's arrogance or pride, you need to reflect upon shortcomings in you that can give rise to a sense of humility. For example, you can think about all the things in the world about which you are completely ignorant. Take the sign language interpreter here in front of me. When I look at her and see the complex gestures with which she performs the translation, I haven't a clue what is going on, and to see that is quite a humbling experience. From my own personal experience, whenever I have a little tingling sense of pride, I think of computers. It really calms me down!