[Advaita-l] Aitareya Upanishad 2.1.1 Bhashya

[Durga Prasad Janaswamy]

Hari Om,

Aitareya Upanishad
2.1.1 Bhashya
अयमेवाविद्याकामकर्माभिमानवान् यज्ञादिकर्म कृत्वा अस्माल्लोकाद्धूमादिक्रमेण
चन्द्रमसं प्राप्य क्षीणकर्मा वृष्ट्यादिक्रमेण इमं लोकं प्राप्य अन्नभूतः
पुरुषाग्नौ हुतः । तस्मिन्पुरुषे ह वै अयं संसारी रसादिक्रमेण आदितः प्रथमतः
रेतोरूपेण गर्भो भवतीति एतदाह — यदेतत्पुरुषे रेतः, तेन रूपेणेति ।

"Then he falls on the earth as rain and enters into cereals, plants or
other edibles. With the food, he goes into a human body and becomes semen,
which is the essence of the food."

I was told that there are many obstacles from the point of reaching earth
as rain and entering into human body with food. And these obstacles are
discussed in detail at some other place.

Any references where these obstacles are discussed in detail?

Thanks and regards
-- durga prasad