Mantra or any holy name of a god is a vibration, Just like in the radio we adjust the frequency to listen a particular radio station for entertainment similarly we use mantra or holy names to adjust our frequency to attain Supreme Bliss. Just like there is a particular frequency on which there is a radio station on which we listen music for entertainment and rest of other frequencies are nothing but noise similarly objective of this human life is tune into that frequency of Supreme bliss so that we can escape the infinite cycle of birth and death and either merge with the formless god if the devotee follows gyan marg or goes under the service of the supreme god if the devotee follows bhakti marg, In both the cases there is no returning back to this world in any form. Any mantra or holy name is that station where there is Supreme bliss and rest everything is nothing but a useless noise. We have to remain in that frequency for a long time so as that we don’t have to intentionally repeat mantra or holy name but they are going on automatically which is ajapa jap. As our body is 60% water and each and every word we speak has a vibration associated with in and an impact on conscious and subconscious level of our body and if we repeat that mantra or holy name then we start to achieve that bliss and there are patterns for every vibration, Like the vibration of a bad word is different and a good word is different and similarly the patterns formed in our body by Holy names or mantra are totally different and after constant repetition of that word, There is a time when we don’t need to do it anymore its going on itself as the patterns have become permanent and we are now in infinite Supreme Bliss 24x7 without even chanting on our own as there are patterns build up in conscious and subconscious which are doing it even in our sleep.
So that we can achieve the level ajapa jap there are rules like 11malas, 16 malas, 21 malas etc