"There is lots of interesting theology about angels, and in some ways we've kind of lost the knack for that," said John Cavadini, chair of theology at the University of Notre Dame.

"We tend to think of angels as things that we'd find in a Hallmark card," Cavadini added. "But many people, especially in antiquity, were very interested in them"—in what they might look like, how they might organize themselves, how they behave.

In the Bible angels served as envoys of God—angelos being Greek for "messenger." Other than that, the scriptures leave a lot of room for interpretation.

"There isn't a lot of detail, and that's the fascinating thing," said Ellen Muehlberger, a professor of Middle Eastern studies at the University