Repetition of any Mantra or Name of the Lord is known as Japa. Japa is an important Anga of Yoga. It is a spiritual food for the hungry soul. Japa is the rod in the hand of the blind Sadhakas (aspirants) to plod on the road to Realization. Japa is the philosopher's stone or divine elixir that makes one God-like. In this iron age, practice of Japa alone can give eternal Peace, Bliss and Immortality.
Japa is repetition of the Mantra. Dhyana is meditation on the form of the Lord with His attributes. There is meditation or Dhyana with Japa (Japa-Sahita-Dhyana); there is meditation or Dhyana without Japa (Japa-Rahita-Dhyana). In the beginning you should combine Dhyana with Japa. As you advance the Japa drops by itself; meditation only remains. It is an advanced stage. You can then practice concentration separately. You can do whatever you like best in this respect.
Name (Nama) and the object (Rupa) signified by the Name are inseparable. Thought and word are inseparable. Whenever you think of the name of your son, his figure stands before your mental eye, and vice versa. Even so when you do Japa of Rama, Krishna or Christ, the picture of Rama, Krishna or Christ will come before your mind. Therefore Japa and Dhyana go together. They are inseparable.
Do the Japa with feeling. Know the meaning of the Mantra. Feel God's presence in everything and everywhere. Draw closer and nearer to Him when you repeat the Japa. Think He is shining in the chambers of your heart. He is witnessing your repetition of the Mantra as He is the witness of your mind.
This article was excerpted from the book Japa Yoga.http://www.dlshq.org/teachings/japayoga.htm