‘As for Nianfo [practice of mindfulness of the name of Amitabha Buddha – “Amituofo”], if the mind is difficult to be unified as one [without being scattered, you] should gather in the mind with sincere mindfulness [of Amituofo’s name], which will naturally be able to unify it as one [to be wholehearted (and thus single-minded) without being scattered (一心不乱)].
The method to gather in the mind, is none other than to first have utmost sincerity [and earnestness; for if the] mind is not utmost sincere, [even if] desiring to gather it, there is no way.
If with utmost sincerity already, but yet to be purely singular [in mindfulness, you] should gather in the ears with attentive listening. Regardless of aloud or silent recitation [during Nianfo], all must be recitation that arises from [the utmost sincere] mind, with the voice from the mouth exiting, and its sound from the ears entering.
(For silent recitation, although there is no opening of the mouth to recite, however, within the mind ground, there is still also the “form” of the mouth reciting [and thus the mental sound that exits for entering the mental ears].) [However, there is no need to visualise this, as you should only sincerely recite and sincerely listen to your sincere recitation.]
With the mind [and thus the] mouth reciting very clearly, and the ear root listening very clearly, thus gathered is the mind, and false [or stray] thoughts will naturally cease.’
– Pure Land Tradition’s 13th Patriarch Great Master Yinguang
(Fourth reply letter to Gao Shaolin)
Summary: To gather in (or calm and concentrate) the mind to prevent scatteredness (due to having stray thoughts), there should be utmost sincere (wholehearted) reciting and listening to one’s own Nianfo, be it aloud or silent.