The killing of Vritra is not one hymn but a refrain running through the whole collection. Indra is called Vritrahan, the smasher of the obstruction, more often than he is called anything else, and hymn after hymn returns to the same sequence: the soma is pressed and drunk, Tvashtr fashions the vajra, Indra strikes the serpent lying on the mountain, and the waters go.
What is released is more than water. The hymns say that with the same blow he found the sun, generated the dawns, propped apart heaven and earth and made the world habitable, so the act is cosmogonic rather than meteorological. Readings that treat it as the monsoon breaking, or as ice releasing mountain rivers, capture something the imagery supports without exhausting what the poets claim for it. What the myth describes in every case is the same structure: an inert mass that holds back movement, and a blow that starts the world running.
Comparative philology has shown that the sentence itself travels. The formula joining a hero, a verb of smiting and a serpent is reconstructible across Indo-European poetic traditions, from the Vedic slaying of Vritra to the Avestan Verethragna, whose name preserves the same compound, and onward into Greek and Germanic dragon killings. The individual monsters differ; the phrase does not.
That makes Vritra unusually important for a figure with almost no character. He is barely described, has no genealogy in the oldest layer and does almost nothing except lie there, and he is nevertheless the thing against which the chief god of the Vedic pantheon is defined.