The efficiency of the Japa is accentuated according to the degree of concentration. The mind should be fixed on the source. Then only you will realize the maximum benefits of a Mantra. Every Mantra has a tremendous force. A mantra is a mass of Tejas or radiant energy. It transforms the mental substance by producing a Particular thought movement. The rhythmical vibrations produced by repeating the Mantra, regulate the unsteady vibrations of the five sheaths. It checks the natural tendencies of objective thought of the mind. It helps the spiritual power and reinforces it.
Mantras cannot be concocted or tailor-made for the individual, despite some current claims. They have always existed in a latent state as sound energies. Just as gravity was discovered but not invented by Newton, Mantras were revealed to the ancient masters. They have been codified in the scriptures and handed down from guru to disciple. Although it is customary for the guru when giving initiation to accept voluntary offerings of fruit, flowers or money, the selling of Mantras is strictly against all spiritual rules.
Neither Mantra, deity nor guru, once chosen, should be changed. There are many paths up the mountain. Perseverance on one alone will bring the aspirant to the top faster than if he were to spread his energies in exploring all the alternative paths.