What happens when you meditate?
The art of meditation has a long prolonged positive effect on human behaviour and thinking. The mind is equated to a jumping monkey that doesn't remain quiet. The restlessness that it builds can lead to health issues and sometimes uncontrollable behaviour.  In general, meditation is to calm the mind and becoming the spectator or observer of the thoughts that rise in your consciousness. 

Now, let's break it down further ...

It first starts with understanding of the 'self' which can be equated to mind in loose terms. Experiences happen to you in your waking state and the mind first starts labelling things. Negative experiences are profoundly deep rooted then positive ones. All these experiences gradually defines how you react to situations that shapes your individual personality. Do you know that there is a spectator within your mind more like a dual personality? it is the subject - object thing. The spectator within you is the observer of things and is often neutral.

Idea of meditation is to remain a spectator for long periods of time and let fewer and fewer thoughts arise into your conscious state. At the end it leaves you a with a sense of accomplishment because as a spectator you're waiting and this deliberate attempt makes the thought (referred as devil) disappear.