Meditation is the gym for the mind. When we exercise our body, it becomes stronger. The same is true for the mind. We train our mind in "skilful mental states", which include things like concentration, presence, awareness, kindness and compassion. Abiding in skilful mental states makes us feel better and helps us grow.

The benefits that we want to see from meditation, be it less stress, less depression, less anger-insert your reason here-are all by-products of skilful mental states. We don't practice being calm, we practice concentration, and from that ability to remain concentrated and single-pointed in our awareness, calm and tranquility emerge. You can read more about skilful mental states here.