阿彌陀經疏 1.247

1.247

經曰：「為諸眾生說是一切世間難信之法」，次第四釋讚授祕法也。一切世間難信之法者，謂一日乃至七日念佛，即拔塵滓高昇淨境，微因著果俗情難信，人恐如來引接之語，故言難信之法。

The sūtra says: '...and for the sake of sentient beings preach this Dharma that is difficult for all the world to believe.' Next, the fourth part of the commentary explains praising his bestowing the secret method. 'Dharma that is difficult for all the world to believe' means that by remembering the Buddha for one day up to seven days, one is pulled out of the defilements and elevated to the pure realm. A subtle cause yielding a prominent fruit is difficult for worldly sensibilities to believe; people fear it is merely the Tathāgata's expedient words to guide them, hence it is called a Dharma difficult to believe.