I am not in favour of japa which is exclusively external in character, though I too advise japa in certain cases, but they are of different type. These are really the means by which an abhyasi is to try for his growth himself. (SS-28)
I am not opposed to japa but I do not approve of the ways in which it is generally practised. Japa does not mean parrot-like recitation of certain words or phrases without any understanding of their real significance, and without any collaboration of thought. In our system too japa is sometimes advised when required, but it is of a different nature, and practised in quite a different way. For example, Gayatri japa is one of the essential features of general Sadhana and is practised by most, irrespective of other japas which might have been advised at times. The way in which it should be done is as follows. The abhyasi is to sit in a meditative mood, repeating the mantra mentally twice or thrice, keeping in view the sense it conveys. He is then to begin meditating upon the sense. The words will naturally go out of his Consciousness and the thought alone will remain in his mind. After some time when he gets absorbed in it, the thought too shall vanish and nothing shall remain except absorbency in the prayerful mood. That is the proper way. Japa practised in this way will be of highest value and immensely helpful to the spiritual growth of the abhyasi. (SS-62,63)
My humble opinion is that few persons perhaps might be knowing the correct process for practising japa. Most of those who happen to come to me are found to have created in their heart a rigid knot by their wrong way of practice, so that it becomes a very hard task for me to remove its effect settled in their hearts in the form of solidity and grossness which, in certain cases, I have not been able to wash off over the course of years. So long as the method of practice is not subtle, the realisation of the subtlest can never be possible. (SS-265,266)