[Acolyte]

Another factor here is that celestials, unless they need to be active in the Marches, don't sleep. And didn't sleep in Heaven, and rarely were created and pushed onto Earth the next day.

I just generally assume that when not working for their Word or on current plans or fighting the opposition, celestials are learning as much about humanity as possible from TV, watching people in cafes, and from listening in on conversations in the subway. And before they came to Earth they spent years and years talking with the souls of the dead and observing from afar.

And note that celestials are typically much smarter than humans. To memorize a jingle we need to hear it a lot (unless Eli wrote it...), but an angel might remember the name of every minor character to appear on an episode of Friends.

What this means for me and in the games that I run is that celestials don't appear egregiously out of place, having picked up a good amount of things, but are always a little bit off, with humorous gaps in knowledge or with a poor ability to differentiate between what someone on a TV show would do and what a real person would do in a given situation. And it means that angels are at a disadvantage dealing with really selfish people (as the people they knew in heaven weren't selfish), and vice versa for demons (how much can you learn from someone when your job is dunking him in a pit of lava until he gives you some Essence?).

Generally, though, Roles and "basic training" provide for celestials to superficially fit in with humanity, though a Soldier who knows several celestials might be rolling his eyes a lot and only the most experienced, humanlike celestials will appear perfectly natural.