But know that by which all this is pervaded is indestructible. No one can make that which is immutable destroyed

The imperative viddhi (know, know!) is direct. The ātman is avināśin (indestructible) — privative of vināśa (destruction). It is that yena (by which) everything is tatam (expanded, pervaded, permeated) — the substratum that sustains manifestation.

Avyayasya (of the immutable, of that which does not diminish) — the ātman is not only indestructible, it is inexhaustible, not consumed. Na kaścit (no one) can kartum (make) vināśam (destruction).

The argument is ontological: by definition, the indestructible cannot be destroyed. Death is impossible for the ātman.