Here are the key conceptual passages I noted down last time I read it:
“When any mental state arises strongly enough to distract you from the object of meditation, switch your attention to the distraction briefly. Make the distraction a temporary object of meditation... You switch your attention to the distraction only long enough to notice certain specific things about it. What is it? How strong is it? and, how long does it last? As soon as you have wordlessly answered these questions, you are through with your examination of that distraction, and you return your attention to the breath.”
“[D]istractions are actually the whole point. The key is to learn to deal with these things. Learning to notice them without being trapped in them. That's what we are here for. The mental wandering is unpleasant, to be sure. But it is the normal mode of operation of your mind. Don't think of it as the enemy. It is just the simple reality. And if you want to change something, the first thing you have to do is see it the way it is.”
“Whatever it is, don't try to repress it. Don't try to force it out of your mind. There's no need for that. Just observe it mindfully with bare attention. Examine the distraction wordlessly and it will pass away by itself. You will find your attention drifting effortlessly back to the breath. And do not condemn yourself for having being distracted. Distractions are natural. They come and they go.”
“From the point of view of mindfulness, there is really no such thing as a distraction. Whatever arises in the mind is viewed as just one more opportunity to cultivate mindfulness. Breath, remember, is an arbitrary focus, and it is used as our primary object of attention. Distractions are used as secondary objects of attention. They are certainly as much a part of reality as breath. It actually makes rather little difference what the object of mindfulness is. You can be mindful of the breath, or you can be mindful of the distraction. You can be mindful of the fact that you mind is still, and your concentration is strong, or you can be mindful of the fact that your concentration is in ribbons and your mind is in an absolute shambles. It's all mindfulness. Just maintain that mindfulness and concentration eventually will follow.”
“The purpose of meditation is not to concentrate on the breath, without interruption, forever. That by itself would be a useless goal. The purpose of meditation is not to achieve a perfectly still and serene mind. Although a lovely state, it doesn't lead to liberation by itself. The purpose of meditation is to achieve uninterrupted mindfulness.”