This simile emphasizes the people should leave their cities and live in the rocky cliffs to hide from their enemies. (See: [[rc://en/ta/man/translate/figs-simile]])
Here "mouth of a hole" is an idiom that means the entrance to a cave. AT: "the entrance to caves" or "an opening in the rocks" (See: [[rc://en/ta/man/translate/figs-idiom]])
# We have heard
Here "We" refers generally to all the people in the surrounding area.
# arrogance ... haughtiness ... pride ... self-glory ... conceit in his heart
All of these words have similar meanings. They are used together to emphasize the extreme pride of the people of Moab.