Mantras are powerful sounds. Mantras are the ones that have when chanted produce great effects. These are chanted repeatedly and that is called Japa. Japa is a key part of Hindu prayer.
Mantras are very rich in their meaning. While doing
Japa one can meditate on the mantra and its meaning. As the mind dwell more and more into that, the mantra conditions the mind and takes up to the higher states and forms the path to the great liberation - eternal bliss !
What makes mantras so special as compared to the normal words ? Mantras are not human composed. One may wonder how can that be possible. Especially given that there are sages associated with the mantras ! The point to be noted is that these sages are not composers of these mantras, as we
normally compose the sentences; they are not the inventors, but they are the discoverers of the mantra. They get to know the mantras in a state in which these words do not emanate from their thoughts, but they are just passive audience to it. Those who go deep in meditation and realize God may be able to get a feel of this situation.