Concentration we have seen twice before, and we will see it again in much more detail in Part III. One of the challenges of deep tranquility is keeping the mind concentrated. This may seem like a direct contradiction of what I have just said, but there may be stages of practice where there can be so much tranquility that the mind can get quite dull and hard to focus. So, just as tranquility is good for concentration and acceptance, too much is similar to not having enough energy. Remember, balance and strengthen, strengthen and balance.
As these are the Seven Factors of Enlightenment, they apply directly to insight practices, training in wisdom. Thus, the concentration being referred to here is a very different kind of concentration than that used for attaining high concentration states. It is called “momentary concentration.” In the context of insight, concentration really means that we are able to very consistently investigate each sensation that arises, one after the other. In this way, we have stability of our ability to investigate, in that it can happen again and again without interruption, but we are not trying to attain stable states or anything else, as we are doing insight practices.