From The Letters of Rennyo Shonin (Gobunsho) Fascicle 3, Letter 2
The teachings of the various sects differ, but since they were all [expounded] during Śākya[muni]’s lifetime, they are indeed the incomparable Dharma. For this reason, there is absolutely no doubt that people who practice them as prescribed will attain enlightenment and become buddhas. However, sentient beings of this last [Dharma] age are of the lowest capacity; this is a time when those who practice as prescribed are rare.
Here [we realize that] Amida Tathāgata’s Primal Vow of other-power was made to save sentient beings in such times as these. To this end, [Amida] meditated for five kalpas and, performing practices for numberless kalpas, vowed that he would not attain perfect enlightenment unless sentient beings who commit evil and lack good reach buddhahood. Completely fulfilling that Vow, he became the Buddha Amida. Sentient beings of this last [Dharma] age can never become buddhas unless they deeply entrust themselves to Amida, relying on this buddha’s Primal Vow.
How do we entrust ourselves to Amida Tathāgata’s other-power Primal Vow, and what frame of mind should we have to be saved?
Entrusting ourselves to Amida simply means that those who truly know what other-power faith is will all be born in the Land of Utmost Bliss, ten people out of ten.
Then what is that other-power faith?
It is simply “namu-amida-butsu.” Fully knowing the meaning of the six characters “na-mu-a-mi-da-butsu” is precisely what other-power faith is all about. We must, therefore, thoroughly understand the substance of these six characters.
To begin with, what do the two characters “na-mu” mean?
“Na-mu” means relying on Amida singleheartedly and steadfastly, without any contriving, and entrusting ourselves without double-mindedness [to Amida] to save us, [bringing us to buddhahood] in the afterlife.
Then, what do the four characters “a-mi-da-butsu” mean?
“A-mi-da-butsu” means that, without fail, Amida sends forth from himself light that illumines sentient beings who rely on him singleheartedly and are free of doubt, as explained above. He receives them within that light, and when their span of life comes to an end, he brings them to the Pure Land of Utmost Bliss. This is “a-mi-da-butsu.”
According to what is commonly said about the nenbutsu, people think they will be saved if they just repeat “Namu-amida-butsu” with their lips. That is uncertain. There are, however, some within the Jōdo school who teach this. Let us not judge it as right or wrong. I simply explain our tradition’s way of faith (anjin), which was taught by the founder of our sect. Those who have [good] conditions from the past should hear this and promptly attain [assurance of] the birth that is to come in the Land of Utmost Bliss. Those who understand this should say the Name of the Buddha; [remembering] the benevolence of Amida Tathāgata who readily saves us, they should repeat the nenbutsu, saying the Name of the Buddha in grateful return for the Buddha’s benevolence, which we receive beyond measure.
Respectfully. Written on the fifth day of the eighth month, Bunmei 6 (1474).