Chanting is not a mindless activity. Srila Prabhupada says that the Lord’s holy name transcends the mind and intelligence because it has descended from the spiritual world and is nondifferent from the Lord. However, if we want to progress in chanting, we have to engage the mind and use our intelligence to follow the correct process. If we do not follow this process, we can chant mindlessly for many births and never attain the real goal of chanting.
(LFD, Vol2, Chanting Purely, Pg 103, 2nd paragraph)