維摩經略疏垂裕記 3.134

3.134

二、竪窮心源修因，二：初、敘意分章。「十三番相資成淨土因」者，荊溪云：初資第二，乃至十二資於十三。細尋具如下解釋中。「上從直心」等者，上釋諸行。諸行相望，故名為橫。一一皆從世間至圓，其義雖竪，但經一往直列而已，終成橫行。況雖竪釋，但約教判淺深不同，是故窮源研於心念，令從淺行直見深理方乃名竪。

Second, cultivating causes by vertically exhausting the source of the mind, in two parts: first, recounting the intent and dividing the sections. Regarding "the thirteen turns mutually supporting to form the causes of the pure land," Jingxi says: "The first supports the second, and so on up to the twelfth supporting the thirteenth. The fine details are fully given in the explanation below." Regarding "from the straight mind above," and so forth, above the various practices were explained. The various practices stand in horizontal relation to each other, hence called horizontal. Each proceeds from the worldly up to the perfect; although its meaning is vertical, the sūtra merely listed them directly in a preliminary way, so in the end they constitute horizontal practices. How much more so since, although vertically explained, they merely judge differences in shallowness and depth according to the teachings; therefore, exhausting the source and examining thoughts in the mind, causing one to directly see the deep principle from shallow practice, is only then called vertical.