The fact that Heaven and Hell are in an office building (the same office building, no less) puts their interactions with humanity in a new light. Heaven is like a company that has found it profitable to be good to its "customers," but it doesn't actually care about them; when push comes to shove, the company throws everyone else under the bus for their own interests. Hell, on the other hand, not only finds it more profitable to screw over its "customers," but encourages the dog-eat-dog employee workplace environment that corporations are infamous for.
When Crowley hears that Jesus is being crucified for his message of "Be kind to each other," he sadly understands rather than expressing bewilderment or horror. Of course he understands, Crowley regularly works with other demons who would be violently offended at the suggestion of showing kindness.
The audience is shown that Heaven and Hell's "Great Plan" is not in line with the Ineffable Plan in the first episode. The third-person omniscient narrator identifies herself as God and explains that she doesn't play dice with the universe—her game is similar to an incredibly complex game of poker, where no one else knows the rules. The show then explains the mistake with the baby swap via the visual metaphor of a dealer performing a shuffling trick that puts the card representing the Antichrist where no one expects him to be, accompanied by God's narration. While she never says anything explicitly (which would be pretty out of character), God is giving the audience insight into one of her card games and showing that, no matter what Heaven and Hell plan, her Ineffable Plan is that the Antichrist will grow up as any other human and have a choice in his future.
While both Heaven and Hell have clearly decided what to do with Crowley and Aziraphale long before, it's interesting that Hell at least goes through the motions of giving Crowley a trial, while Heaven does not do the same for Aziraphale. It could suggest that the archangels are so convinced they can't do wrong that they don't see a reason to second-guess their decision in any way, to the point that nobody even answers when Aziraphale asks if he couldn't persuade them to reconsider. Beelzebub, on the other hand, gives Crowley a, however tiny, chance to change their minds.
Alternately: demons are used to double-dealing and manipulation, while angels are repeatedly shown to be gullible and take things at face value. Of course demons would think Crowley had more to say or some kind of plan, while angels would assume the worst of Aziraphale without question. "Not questioning" is the reason they're still angels after all.
Another interpretation: Hell is a land of chaotic evil demons looking for a spectacle and they never actually intended to give Crowley a chance to make any points, they just wanted to watch him squirm at a trial and then be executed, while Heaven is a land of lawful "good" (aka an authoritarian dystopia) and the angels are just concerned with getting the trouble maker out of the way as fast as possible so they can go back to being orderly.
Crowley is only getting a trial the same way that Josef K. is getting a trial. Notice that instead of a defence counsel, he gets a person making sure none of his misdeeds are forgotten. It's a farce and a mockery of justice intended to make him squirm - notice how the bathtub is already waiting in full view - in front of an audience of other demons. There is clearly zero intention of taking anything he says into consideration. The demons are just twisting the knife.
The exchange between Adam and his mother in the last episode is a direct parallel to the original events in Eden on a smaller scale. Like God, Deirdre is a loving parental figure choosing to let her child go out into the garden, even though she knows hes probably going to disobey her one instruction. Sure enough, Adam mimics his namesake, disobeys, and leaves the garden, even stealing an apple on the way. The narration also drives home the parallel, suggesting both acts of disobedience to be Worth It.
It makes perfect sense for War to be carrying Aziraphales flaming sword. It was the first weapon ever wielded by mankind, after all.
Aziraphale and Crowley talk with each other during most of the "To be, or not to be" monologue. They stop and listen when it mentions "the pangs of despised love", and "the insolence of office". Their inability to acknowledge their mutual feelings (either romantic or of good friendship) and the bullying from their respective Head Offices are the two things that keep on getting in their way.
Crowley's utter heartbreak when he finds Aziraphale's bookshop in flames might seem a little over the top considering angels and demons can't really die by conventional means and their bodies just end up being discorporated. Until we get to the last episode and see that the demonic equivalent to holy water is hellfire. Crowley probably thought that someone had used hellfire to render Aziraphale Deader Than Dead and set the shop on fire in the process. And just to twist the knife, the last words he'd said to Aziraphale were, "I won't even think of you!"No wonder he was so crushed!
Especially if you consider that Aziraphale's phone receiver was lying on the floor as if dropped in a panic and Hastur's habit of setting buildings on fire, Crowley might have assumed Hastur escaped through Aziraphale's phone line and killed him, burning down the shop in the process.
Gabriel is traditionally the angel who informed Mary that she was pregnant with Jesus. Just imagine this version of the Archangel Gabriel breaking that news to poor Mary.
Aziraphale and Crowley laugh off their body-swap with an air of Angst? What Angst?, but when you stop and think about it, the risks they took were massive.
They are completely and utterly alone among their enemies of millennia, and each has to trust the other to pull off the trick while having no way to assist if something goes wrong. Plus, if either slips, they're both doomed. No pressure then.
If their trick was discovered, each was stranded on the side that had the most access to his fatal weakness.
Hell being Hell, Aziraphale had no guarantee that they'd do anything quickly. He could easily have been tortured, and keeping up the charade through that would have been extremely difficult.
Meanwhile, Crowley's dragged back up to Heaven. While not as overtly threatening as Hell, that had to be traumatic for a fallen angel.
Then add the worry for their friend. These are two beings who've been shown to care deeply for each other. Aziraphale's flat "That's holy water" and Crowley's reaction to the hellfire have an air of barely restrained horror — not for themselves, but from the idea that this is the fate that awaited their partner. We've already seen what holy water can do, and Aziraphale's fear that Crowley would use holy water as a suicide pill — imagine how it would feel to sit there, wearing your best friend's face, knowing that your worst nightmare was so close to coming true.
And then there's what must have happened after their trials were over. It's unlikely that Aziraphale and Crowley were dropped back on Earth at the exact same time, so it is likely that one of them was stuck waiting on that park bench for a bit, worried sick and hoping that the other made it safely as well, all while still having to stay in-character in case anyone was watching.
There was also no guarantee that Heaven/Hell would be freaked out enough to simply stop after the holy water and hellfire failed to work. Even if they couldn't pull a Cessation of Existence on them, there's still the possibility of inflicting a Fate Worse than Death. That line Aziraphale drops about "eternity in the deepest pit"? That was a real possibility.
As horrible as it is, Crowley being on trial — and even being sentenced to execution — makes a grim sort of sense. The audience is shown that Crowley is basically a good (and at times, even sweet) person/being — but he kills Ligur in a particularly horrific way. It's self-defense, yes, but it's one of the few perma-deaths in the show.
That said. Crowley does have morals. He must have been exceptionally afraid of the fate that awaited him in Hell if he was prepared to play this particular trump card.