What, then, is concentration meditation? What is insight meditation? How do they differ? Concentration meditation, in the first place, is better called the mental development (bhāvanā) of concentration (samādhi).
This is training the mind (citta) to focus on a particular object, for instance, the breath as we breathe in and breathe out. When the mind focuses in this way, it brings itself to a point. The result of this training is the development of tranquility. The body, and along with the body the mind, calm down. We develop the ability to focus the mind on one thing rather than simply let it jump around uncontrollably from one thing to another. Insight meditation, on the other hand, is the mental development of insight (vipassanā), i.e., intuitive, firsthand seeing into the workings of the mind and into the nature of the world (cf. in-sight).
It is important to note that the term vipassanā is used in two senses in the literature: as the type of meditation (actually, vipassanā–bhāvanā) and, more precisely, as the insight that is achieved through this meditation practice. So, both concentration meditation and insight meditation result in something: in the former case a state of tranquility, in the latter case insight into the ultimate nature of things. In this sense both of these practices are tools for the improvement of the mind. What is more, they are tools that are developed through the meditation practice. This is “on the job” training: the way to get good at it is to just do it. Furthermore, both types of meditation work together: concentration meditation affords the tranquil state that is conducive to the mind’s ability to see into the reality of things. Because the mind can view things as they really are, it can clear up the problems that it otherwise causes for itself and live in peace and in harmony with the world.
Insight meditation is of the utmost importance. It is not a sometimes sort of thing, something done, for example, in a meditation retreat once in a while. It is not a special practice for monks or nuns, something not feasible for the rest of us in the workaday world. It is not a thing to take or leave, but a duty to perform if we are to live in conformity with the laws of nature, i.e., of the totality of the world of human experience. It is a natural process, one of gradually letting go of the world, both of what we like and what we dislike. It is the way all of us are supposed to live in order to achieve, ultimately, the highest spiritual perfection available to human beings, Enlightenment (nibbāna).