Tatsabhavyapattirupapatteh III.1.22 (313)

(The soul when coming down from the sphere of moon) attains similarity of nature with them, (i.e., with ether, air, etc.,) as this only is possible.

Tatsabhavyapattih: attainment of a similarity of nature with them; Upapatteh: being reasonable.

The way of descent of the individual soul from the sphere of the moon is now discussed. The Sruti declares, "They return again the way they went, to the ether, from the ether to the air. Then the sacrificer having become air becomes smoke, having become smoke he becomes mist, having become mist, he becomes a cloud, having become a cloud he rains down" (Chh. Up. V.10.5 & 6).

Now a question arises whether the soul actually becomes identical with ether, etc., or simply resembles them.

This Sutra says that the souls do not attain identity with them, because it is impossible. It is not possible that one thing should become another in the literal sense of the word. One substance cannot become another. If the souls become identical with ether, they could no longer descend through air. The souls become only like ether, air, etc. They assume a subtle form like ether, come under the influence or power of air and get mixed with or connected with smoke etc. The attaining to the state of being smoke, etc., is but moving along with them when they are in motion, stopping while they stop, entering into them and becoming as light as they are. Therefore the passage means that the souls become similar to Akasa, air, etc., but not identical.