571 Angelology

The word angel is a descriptor for an activity not the title of a class of beings. Most of what many Christians have been taught about celestial beings, including ones tasked with "delivering messages" (angels), doesn't come from scripture. the Bible never uses the phrase "fallen angels" nor does it ever identify demons as being fallen angels or even as celestial beings. So where did the ideas in Angelology come from, about the hierarchy in the celestial realm?