It can be easy to think that all we need to do to walk the Noble Eightfold Path is to be mindful. Although mindfulness is the cornerstone of all Buddhist practice, it alone is not enough. We want to be mindful of what is happening, and then investigate what is happening. One form of investigation is to notice whether there is reactivity or Equanimity in the heart/mind in relation to whatever it is that we are being mindful of. The clear comprehension part (or at least one aspect of clear comprehension) is to know what our relationship is to the object of mindfulness.
For example, we might hear a sound that registers as pleasant to us. Say, a song bird's call. We can be mindful of the sound and its pleasant nature. We can also go one step further and see if there is any reactivity in the heart/mind in relationship to that sound. Do we wish it would stop because it’s bothering us? Do we hope it continues because it sounds so lovely? If so, there would be reactivity in the form of aversion or desire. We can know that clearly. Not judge it, or make ourselves wrong for it, but simply know there is reactivity in the heart/mind. Perhaps notice how that feels in the body.
This is not an intellectual exercise. It’s about connecting with what is arising, staying connected to it, and noticing (not thinking about) our relationship to it. Why is this important? The teachings say that if there is greed, hatred or delusion in the heart/mind, there will be suffering. Of course, we want to know this in our own experience. Therefore, we want to know if these defilements are present in the mind, so that we can do something about it, and avoid or mitigate any suffering. On the other hand, if there is Equanimity (non-reactivity) in the mind, the teachings say this will lead to happiness. Again, we want to know this in our own experience.Therefore, if Equanimity is present, we want to know it clearly, because the way to strengthen a wholesome mind state (one that leads to happiness) is to be clearly aware of it.
This practice of Mindfulness and Clear Comprehension really is at the foundation of our practice of cultivating conditions that are supportive of unconditional, lasting happiness.