Japa is a training by which the ever-dancing rays of the mind are compelled to behave in some order and rhythm, and bring out of their co-operative effort, a single melody of repeated Mantra-chanting.
In thus practicing, the mind becomes extremely single-pointed. In fact, Japa properly done can more effectively bring about a sustained single-pointedness than all the hasty methods of meditation.
A mind seasoned with Japa is like tinned food, which is ready for consumption after a few seconds of warming-up on the fire. A short period of meditation can take a Japa-conditioned mind to unimaginable heights in an impossibly short time.
(Source: Kindle Life by Swami Chinmayananda)