When chanting the Hare Krsna maha-mantra, in the beginning one may commit many offenses, which are called namabhasa and nama–aparadha. In this stage there is no possibility of achieving perfect love of Krsna by chanting the Hare Krsna maha-mantra. Therefore one must chant the Hare Krsna maha-mantra according to the principles of the above verse, trnad api su-nicena taror api sahisnuna. One should note in this connection that chanting involves the activities of the upper and lower lips as well as the tongue. All three must be engaged in chanting the Hare Krsna maha-mantra. The words "Hare Krsna" should be very distinctly pronounced and heard. Sometimes one mechanically produces a hissing sound instead of chanting with the proper pronunciation with the help of the lips and tongue. Chanting is very simple, but one must practice it seriously. Therefore the author of Sri Caitanya-caritamrta, Krsnadasa Kaviraja Gosvami, advises everyone to keep this verse always strung about his neck.
Cc Adi 17.32, Srila Prabhupada's full purport