abstractly::Mantra is a process to control'niyantran' your mind--'mann'.
They are written by enlightened people who perceived the divine light within their inner self.
Proper recitation of mantras i.e. with the knowledge of their meanings motivates you to go in the shelter of The Perfect Master from whom you can learn the art of mind control and that will lead you to salvation. Moreover, when prononced with pure and selfless heart, it may lead to various positive changes in your health and environment also.
gayatri mantra, Om Namah Shivaay, Shanti mantra....