I thought meditation does not only work on mind and soul, but it is more than that.
Meditation in English is a loose word - it can mean so many things including Dharana, Dhyana or Samadhi. Meditation is not an act (initially one starts it as an act) but is actually is a state of existence (where you are completely aware and harmonious).
Let's examine each of these in simple terms:
Dharana: The ability to focus on one thing for elongated periods of time (say hours together).
Dhyana: The ability to contemplate on a topic for hours together
Samadhi:Being one with the object of meditation. This is the state where the Seer and the Seen becomes one. This is the state where Advaita is experienced.
How does it work on Human personality: Well unfortunately personality is just a shallow cloak that humans wear in their day to day social life. It is like the dress that one wears when s/he goes out. So using meditation (henceforth when I use meditation, I mean Dhyana unless otherwise specified) to address human personality (in whatever way) is like using a Jet plane to commute between home and office (within the same city).
Personality is what one acquires as one grows up in society - from people around him/her, situations around him/her and their own reactions to tendencies within them. Whatever it is, it is acquired. It is not even experienced during sleep.
Meditation essentially starts with unravelling the layers of our personality that we have consciously or unconsciously added over our lifetime. This one can do simply by paying attention to what all happens with oneself under various circumstances - how one reacts and whether one is aware that one are reacting while reacting.
Once awareness increases, one can go further deep and unravel the truth that s/he is the all pervading timeless Self. (Please note - soul is a another loose word that cannot be translated directly into the Indian context and hence I'm using Self).
Note: For one to embark on a meditative journey, one must gain command (Asana Siddhi) over their posture. They should be able to sit or remain in one posture (any posture) for more than 2 hours without being bodily conscious.