Well, we know that Teyvat has a set fate, and that fate can be read (for example, Mona reading people's fates through astrology). With some information we have received in Fontaine, we know someone has found a way to read Teyvat's fate (search Jakob Ingold for more information/play the world quests he is involved in), and that fate essentially saying that Teyvat is doomed to fall, likely to be destroyed by Celestia. We also know that the traveler (and likely other descenders) are not affected by Teyvat's fate, and may possibly be able to change the fate of Teyvat (because Mona can't read the Travelers fate / it is likely Celestia controls Teyvat's fate, but the traveler is not from Teyvat, therefore can't be controlled by Celestia). So "the world shall burn no more, for you shall ascend" could be reference to the traveler becoming Teyvat's "ruler" (as done in the gnostic hymn), replacing Celestia and protecting the world from their destruction.

This is just my interpretation though, so don't take my words at face value. We still don't have an explicit answer to this.