There are many regulative principles in the sastras and directions given by the spiritual master. These regulative principles should act as servants of the basic principle — that is, one should always remember Krsna and never forget Him. This is possible when one chants the Hare Krsna mantra. Therefore one must strictly chant the Hare Krsna maha-mantra twenty-four hours daily. One may have other duties to perform under the direction of the spiritual master, but he must first abide by the spiritual master’s order to chant a certain number of rounds. In our Krsna consciousness movement, we have recommended that the neophyte chant at least sixteen rounds. This chanting of sixteen rounds is absolutely necessary if one wants to remember Krsna and not forget Him. Of all the regulative principles, the spiritual master’s order to chant at least sixteen rounds is most essential.

Srila Prabhupada — CC Madhya 22.113 purport