俱舍論頌疏論本 29.33

29.33

釋曰：生上二界總由三緣：一、由因力，謂於先時，近及數習為起因故。二、由業力，謂先曾造感上地生，順後受業，彼業異熟將起現前，勢力能令進起彼定。三、法爾力，謂器世間將欲壞時，下地有情法爾能起上地靜慮，生上二界。起無色定由因、業力，非法爾力，無雲等天無災壞故。生在色界起靜慮時，由上二緣及法爾力。若生欲界，起上定時，於前三緣，更加教力。

The commentary explains: Rebirth in the upper two realms is in general due to three conditions: First, through the power of cause, meaning that previously, familiarity and frequent practice served as the cause for their arising. Second, through the power of karma, meaning that one previously created karma conducive to rebirth in a higher level to be experienced in subsequent lives; when the maturation of that karma is about to appear, its power is able to induce the progressive arising of that samādhi. Third, through the power of nature: when the receptacle world is about to be destroyed, sentient beings of a lower level naturally are able to give rise to the dhyānas of the higher levels and be born into the upper two realms. Giving rise to the formless samādhis is due to the power of cause and karma, not the power of nature, because the heavens such as the Cloudless Heaven are free from calamities and destruction. When one is born in the form realm and gives rise to dhyāna, it is due to the two conditions above as well as the power of nature. If one is born in the desire realm, when giving rise to the higher samādhis, one adds the power of instruction to the previous three conditions.