credentials and authority

If an angel came to earth, how would we distinguish its legitimacy?

Authors and speakers list articles and books in their resumes, which can make them sought after on the lecture tour. Doctors and engineers have letters behind their names, imparting their qualifications and significance.

Credentials give authority, but only if we recognize them. What about unrecognized authority?

What’s an angel to do, if it can’t show its wings?