觀無量壽佛經疏 3.177

3.177

四、從然彼如來下，至必得成就已來，正明凡心狹小、聖量彌寬，注想無由，恐難成就。斯乃不以小故難成，不由大故不現，直是彌陀願重，致使想者皆成。

Fourth, from “yet that Tathāgata” down to “will surely attain accomplishment,” it directly explains that ordinary minds are narrow and small, while the holy measure is vast and broad; focusing thoughts lacks a basis, and it is feared to be difficult to accomplish. Thus it is not that because of being small it is difficult to accomplish, nor that because of being large it does not appear; it is simply that Amitābha’s vows are weighty, causing those who visualize to all attain accomplishment.