Prashna-1-9-saṃvatsaro

Sri Shankara’s Commentary (Bhashya) translated by S. Sitarama Sastri

How the pair—the moon, having form, the food and the prana, the formless, the eater, the sun, could create all creatures is explained. This pair alone is time, the year is the lord of creatures, because the year is accomplished by the pair which together are the lord of creatures; the year being a combination of tithîs, days and nights accomplished by the moon and the sun, is said to be of the nature of the pair, food and eater being no other than they. How is that? Of the year the lord of creatures, are two paths, the southern and the northern. These are the two well-known paths, each extending over six months, by which the sun goes south and north, distributing worlds among those who perform karma alone and those who combine karma with worship. The second tadu, i.e., the tadu in ‘tadupâsate’ is an adverbial adjunct. Those among the Brâhmins and the rest who follow only what is done, as Ishtam (sacrifices) and pûrtam (pious acts) and not what is not made, i.e., nothing eternal, attain the world of the moon, i.e., the world of food, a portion of the lord of creatures, who is both food and eater, the worlds of the moon being in the nature of one made, i.e., not eternal. They, after consumption there of what has been done, return, i.e., enter this world or something worse, as is said. As these devotees, i.e., the house-holders, the seers of heaven, desirous of offspring achieve as the fruit by the sacrificial and pious acts, the moon, i.e., the lord of creatures in the form of food; therefore, they attain what was performed by them, i.e., the food, i.e., the moon to which the southern route leads. This is the food, the moon, to which the route of the manes leads.

Links
Various resources on the Prashnopanishad
Upanishad Series – Kena Upanishad Commentary by Swami Chinmayananda