觀無量壽佛經疏 3.100

3.100

一、從佛告阿難下，至次當想佛已來，正明結前生後。言所以者何者，是其問也。所以須想佛者何。

First, from "The Buddha told Ānanda" down to "next one should visualize the Buddha" directly clarifies concluding what precedes and introducing what follows. The words "Why is this?" are its question: why must one visualize the Buddha?