How does the recitation of the Buddha's name that arises spontaneously in the mind come about? Who is reciting? The spontaneously arising recitation of the Buddha's name is all initiated by the manas (the mental faculty); it is the manas that is reciting. Initially, the conscious mind (mano-vijñāna) is unaware of it. Only upon becoming aware does it find itself unable to control it and cannot help but follow along, listening to the sound of the Buddha's name. The conscious mind's own awareness is volitional awareness, whereas spontaneous awareness is not the conscious mind's own awareness but rather the awareness of the manas, the activity of the manas. This kind of Buddha-recitation samadhi is a state of meditative concentration, and this concentration is relatively stable. Relying on this samadhi state, one then practices the contemplation of the four foundations of mindfulness (satipaṭṭhāna). The mind, being pure at this time, facilitates the practice of contemplation.
The spontaneous emergence of the sound of Buddha recitation, continuously lingering in the heart and mind, is precisely Buddha-recitation samadhi. All kinds of samadhi arise from the manas. Why is the manas able to initiate samadhi? Those whose skill in Buddha recitation is not yet mature will not experience Buddha-recitation samadhi. Those whose skill in various contemplative practices is insufficient will also not experience samadhi states. So-called "mature skill" refers to the successful permeation of the manas through long-term adherence to a specific practice. Once the manas is sufficiently permeated and matured, it automatically and spontaneously recites the Buddha's name and engages in contemplation, giving rise to various samadhi states. The arising of any samadhi is not determined by the conscious mind nor controlled by it. The conscious mind can only passively accept and passively merge into the samadhi state, where it experiences the samadhi and the bodily and mental sensations.