Meditation practice can be quite the reprieve from our busy lives, a quiet time to find a bit of peace of mind. It never really loses that effect, but as we become more familiar with the nature of the mind, the reasons as to why and how we practice begin to broaden.
As we think, so we become. Being as such, whatever we put into the mind, whatever we entertain, comes in through our senses and inevitably comes out through thought, words, or actions. Every state of mind is preceded by a thought. Thoughts are the causal seed for the resultant state of mind. In this way, a thought becomes a state of mind. Therefore, whatever state of mind we experience is dependent on the thoughts we entertain.
Knowing this, how we practice changes in that we become increasingly more aware and exercise more care in choosing what we willfully let in. We start to understand that everything that enters the mind through our senses affects our state of being. What we watch, read, hear, put into our bodies, etc., all for the duration of our exposure and for an immeasurable time thereafter, are affecting our quality of mind. Becoming wise through prior experience, we begin to question whether we want to inherit the consequent state of mind that will arise from our present actions.
Knowing better becomes doing better.
So the why as to why we practice changes. Knowing that what we're seeing in the mind during our seated meditation practice is a direct result of how we're using our minds throughout the day, we now are more inspired not just to seek that peace of mind "on the cushion", but also to make choices that will help better maintain it throughout the day. The reason we practice changes from seeking a temporary reprieve to finding an enduring freedom through willful and kind self discipline both on and off of the cushion.