In short, the apocalypse. The end times. Armageddon.

Well, at least for Christians. Medieval European life was permeated with religious notions. Their view of the future was also deeply influenced by their religious worldview. Judaism has similar notions about the future and so does Islam. Hinduism has a cyclical worldview. The idea of a future that revolves around technological developments, or the notion of progress is a fairly modern idea.

For a more detailed response, see this previous answer by u/sunagainstgold.