Thanissaro Bhikkhu wrote:
Two principles in [the Buddha's] teaching on kamma were especially distinctive. The first is that kamma is intention [AN6:63
]. In other words, action is not simply a matter of the motion of the body. It’s a matter of the mind — and the intention that drives the kamma makes the difference between good actions and bad.
The second distinctive principle is that kamma coming from the past has to be shaped by kamma in the present before you can experience it. You actually experience your present kamma before you engage with the results of past kamma. Without present kamma, you wouldn’t experience the results of past kamma at all. The importance of your present kamma is the reason why we meditate. When we meditate, we’re getting more sensitive to what we’re doing in the present moment, we’re creating good kamma in the present moment, and we’re learning how to be more skillful in creating good kamma all the time, from now into the future.
Now, in learning to shape our present moment skillfully, it helps to learn lessons from other people who have learned through experience how to shape their kamma skillfully themselves. We also have to learn from our own actions, observing what we do and the results of what we do. Once we’ve learned those lessons, we have to remember them. If we learn them and then forget them, they’re useless.
It’s for this reason we need to develop mindfulness, or sati
, which the Buddha defined as a faculty of memory: your active memory, the lessons you need to remember from the past about how to shape your experience skillfully in the present. There are people who explain mindfulness as bare attention or full awareness, but the Buddha wasn’t one of them. In his use of the term, mindfulness is your active memory, your ability to keep things in mind. So, as we discuss mindfulness in the course of this retreat, try to keep the Buddha’s meaning of the word in mind.
From: The Karma of Mindfulness: The Buddha's Teachings on Sati and Kamma
by Thanissaro Bhikkhu