"No, not of the Earth," Castiel corrected. "He is the mighty Creator, sovereign King of the Universe. Your people may have lost their faith, but that does not unmake what is and always has been." Without warning, the bodeful shadow of black storm chased the sky, framed by a modest set of library windows. All the light fixtures went out with a murmur and as the world was thrown into pitch darkness, there was a single clasp of lightning, and in their small corner of the library, three human-shaped silhouettes flashed against the wall. Flanking one of these silhouettes on either sides were enormous wings, unfurling themselves as high as the ceilings would allow.
Having served its purpose, the blanket of gloom died fast, replaced by a perfectly mild weather that smiled down at them as though it had never gone at all. A bit theatrical, perhaps, but most ways of celestial revelations were. Castiel had no great taste for the shadow play personally, but it was necessary in order to avoid fatal consequences for the humans who beheld his true form.
"You are not as old as you think you are," he continued noncommittally, addressing the Doctor by his trueborn name. He was looking into the Doctor rather than at him, clear blue eyes unfocused as though gazing into some distant and tranquil place. "Nine-hundred-and-seven is pittance compared to the age of the universe. You, of all His creation, should know that some of us have existed since before and beyond time."