首楞嚴義疏注經 8.322

8.322

眾生生死本分由情，情著染境，因是從墜。今以淨境為所欲處，但由其想，不屬於情，乃是眾生分外之事，故云外分。氣謂氣色也。

The original share of sentient beings' birth and death is due to emotion; emotion attaches to defiled objects, and through this they sink downward. Now, taking pure objects as the place of desire is solely due to their thought and does not belong to emotion; it is an affair outside the lot of sentient beings, so it is called 'the external share.' 'Vapor' (qi) means atmospheric color.