Bhagavad Gita, Chapter 11, Verse 28

Verily, as the many torrents of rivers flow towards the ocean, so do these heroes in the world of men enter Your fiercely flaming mouths.

A real, familiar image, rivers flowing into the ocean, is used to describe something almost impossible to picture otherwise.

Comparing warriors entering this form to water joining the sea makes an overwhelming sight feel grounded in something Arjun already understands. The scale stays enormous, but the image itself stays simple and real.