觀無量壽佛經義疏 2.66

2.66

「『當起想念，正坐西向。』」起想，即發觀也。正坐，則身儀也。全趺半趺、直身累手，如坐禪法。故《僧傳》中古晉高僧坐不背西，蓋遵此耳。二、示觀相。

"'You should arouse visualization and mindfulness, sitting upright and facing west.'" Arousing visualization means giving rise to the contemplation. Sitting upright is bodily deportment. Sitting in full lotus or half lotus, with an erect body and hands placed together, is according to the method of seated meditation. Therefore, in the Biographies of Eminent Monks, the eminent monks of the ancient Jin never turned their backs to the west when sitting, which was simply in compliance with this. Second, showing the marks of contemplation.