Tranquility. We need a certain amount of calm to investigate, right? So, there are different ways to bring about tranquility. One way can be coming from concentration and one way can be coming from wisdom. The calm that comes from letting go of wrong view on a deeper level is very important because the other type of tranquility only suppresses the hindrances. However, at times when the mind is very, very restless, it can be helpful to know ways to calm the mind sufficiently, so we can then go deeper in order to let go of the hindrances.
There are different ways of balancing The Seven Factors of Enlightenment;. You can look at it as a similar to sleeping and working. We don't sleep twenty-four hours a day and we don't work twenty-four hours a day. We need a balance. So sometimes people investigate a lot, and they can get rather tired, a bit strung out; so they have to realize that that's the time to calm the mind a bit, perhaps by letting go of reflection and calming the mind by observing the breathing, or by letting go of the thoughts, or by using walking meditation. These methods can be how to get a certain amount of calm in those times.
Also knowing which types of reflections that bring a sense of calm can be helpful. Compassion/Lovingkindness can bring a certain level of tranquility and, at the same time, bring insight. Some of the confidence inspiring objects, depending on how you do them, can be more directed towards tranquility or insight. We do need a certain amount of stillness, a certain amount of stability, so that we can see what comes into our focus. This is why in the beginning of a retreat, we ask you to observe the breathing because we don't want you to throw away that particular technique that we have once we get into the reflections, thinking that, "It's just a technique we use until we're sufficiently evolved so that we can use reflection all the time."
We need to balance the factors of enlightenment. We have a certain amount of tranquility, this gives a certain amount of calm to the mind so that we then have the power to investigate. But if we just go to a certain level of tranquility, and we just stay there in the tranquility without investigating, then we don't develop the other factors of enlightenment. Mindfulness supports both because in order to have a certain amount of one-pointedness, we have to be aware of when the mind goes off using one-pointed observation.
Similarly when we're walking, it can be directed towards investigation or it can be directed towards calming. If the mind is particularly restless, we may have to focus more on calming during the walking; that is, just focus on the footsteps, observing the impermanence of things. Then, when the mind is particularly calm and focused, we may broaden out to be aware of the contacts that arise - and see the arising and passing - the impermanence of things.
So Tranquility, a certain amount of calm is necessary to rest the mind; just as sleep is necessary to renew the body. However calm, by itself, won't bring wisdom. Thus we have to understand the limitations of tranquility.