The goals of shamatha practice [Sanskrit: meditative quiescence] are to quiet the noise that bedevils the untrained mind, in which one’s focus darts from one sight or sound or thought to another like a dragonfly, and replace it with attentional stability and clarity. Those two qualities of attention … allow the practitioner to gain insight into the nature of mind and human experience.
To do this, yogis cultivate a sense of mental and physical relaxation from which attentional stability follows. That enables the mind to focus either on an object in the outside world or on a thought or feeling generated within the mind, something that in a person less practiced in attentional training tends to vanish like surf on the sand.
A mind trained in shamantha is better able to resist distraction and feels a sense of peace and calm. Attentional clarity, which follows from attentional stability, is the ability to focus on a chosen object with vividness and in sharp detail, no longer dulled by the boredom or mental fidgets typical of the untrained mind.
Image via Wikipedia
Begley, S. (2007). Train Your Mind, Change Your Brain: How a New Science Reveals Our Extraordinary Potential to Transform Ourselves (1st ed.). Ballantine Books. Ch. 9, p. 214