Shamatha means tranquility, calm or quiessence, and is about developing focused attention by concentrating on an object of meditation such as the breath. It is measured in 9 specific stages, these stages lead to achieving single pointed concentration/meditation.
This form of meditation is a honing tool for focused attention, developing relaxation, stability and clarity. It teaches the use of specific antidotes to counteract the obstacles that arise such as laxity and excitement which hinder the practice of meditation. Training in this way helps to free the mind from disturbing emotions and conceptual thinking processes by disciplining the mind with some degree of single pointed focus, clarity and awareness.
Mental clarity can only come when the mind becomes free from sluggishness, drowsiness, and lethargy/laxity. Mental stability will only come when the mind becomes free from excitement, agitation, rumination and addiction to daydreaming.
The very purpose of Shamatha meditation is not just to feel good for a period of time but to give birth to deeper levels of understanding, of wisdom and by practicing in this style of meditation, the individual is able to gain inner peace, harmony and mental well being and balance.