But the point really, is that if you want some horrifying monster then there's no particular reason why you need to have it be called an angel, is there? When you use a familiar present-day term then readers automatically get a specific mental image. You could just as easily call your monster a Wug from the planet Wuggle and then throw in a bit about how it used to visit the Middle East 3000 years ago to play mind-games with the religious types there.