What is the exact use of japa?

Question: 1. Swamiji, I have a doubt. What is the exact use of japa?? Is concentration the only outcome of JAPA ?? If suppose I am able to get very good concentration in my work, then does that mean JAPA is not necessary?? (I am discussing purely from materialistic point of view). What does JAPA exactly do ??? The one benefit which I clearly see is concentration.
2. My second question is: What is the speciality of a MANTRA (say, Om Namah Shivaya). Why can’t I say, “ABRACADABRA” and repeat it as a Mantra ? Please explain me the science behind this.

Answer: 1. The efficacy of Japa is to purify the mind. If you are concerned only about materialistic point of view, there is no necessity of Japa at all. By constantly doing Japa, more than concentration, it changes the whole personality internally and makes you a better and better man. You will reach a state where your personality will be – “Be good & do good”. When you reach that state, you will have absolute contentment and happiness.
2. The Mantra is the name of the Lord which has been spiritually charged with power by the Guru.