A man takes a lunch break in a grey, artificial plaza with a sickly tree in it, thinking about deforestation. Suddenly the tree starts to grow, sending out roots and tendrils to the cracks in the paving, and the janitor climbs up on a branch and helps the tree break through the glass ceiling, laughing aloud as it begins to rain.
Crowley rushes into the burning building to save his friend - to save Aziraphale.
And relatedly, that when Aziraphale figures out where the Apocalypse will begin, his first instinct is to call Crowley.
He ought to call Heaven. He wanted to call Crowley.
Sergeant Deisenburger being sent away... to the farm where he grew up, and it seems like he's not leaving this time, especially when he hangs up his gun and stops talking like a soldier.
"The tape he put on was Handel's Water Music and it stayed Handel's Water Music all the way home." The perfect finishing touch to everything that had come before.
At the end, Crowley and Aziraphale get their dinner at the Ritz. And meanwhile, a nightingale sings in Berkley Square.
The way Crowley and Aziraphale deal with each other towards the end, e.g. how hands-on they are with each other - Crowley grabbing Aziraphale's arm and whispering to him, Aziraphale laying a hand on his shoulder, etc. Aziraphale expresses genuine sympathy for Crowley's ruined car, whereas Crowley sincerely commiserates on Aziraphale's lost books. This is an angel and a demon by the way, representatives of two opposing sides that hate each other so much that the mere tension between them keeps trying to bring about the end of the world.
Crowley is clearly stressed over the idea that Hell could crush and torture him into nonexistence any time they liked, and while he seems to occasionally take it out on humans by making their lives somewhat miserable, he's still willing to lay his head on the chopping block (despite express warnings by Hell that if something goes wrong, he will be done for) to try and prevent the Apocalypse rather than let all those people die for some cosmic chess game. There's also the fact that the war would mean either his own death or the death of his best friend.
At the end, Crowley and Aziraphale choose to stand together in a futile battle against the Devil to try and postpone the inevitable rather than watch him and Heaven wreak havoc on Earth.
The way that Adam Young's love of his home is depicted is very touching, especially when it brings him back from the brink of bringing about The End of the World as We Know It.
Likewise the fact that an idyllic childhood and life among humans (without any celestial or infernal intervention) was able to overcome Adam's demonic nature and instill a love of the world forms the core of the book. Choice and the potential for good and evil in all of us is a big theme of the book best exemplified in truly heartwarming fashion by Adam Young.
A good example: when Adam meets Anathema, she invites him in, gives him lemonade, and spends the afternoon telling him about paranormal things, which fascinates him to no end. He wants to do something nice for Anathema, just because he likes her, so he uses his powers to shut down a nearby nuclear power plant (which he knew she didn't like).
To add to it: he doesn't shut it down exactly. It's still running perfectly, producing exactly the amount of electricity it ought. It's just that all of the radioactive material that powers the plant has vanished.
The International Express postman's been delivering items to the Four Horse Persons throughout the entire book and having just finished with Pollution realizes his next stop is Death. Before he goes to meet him, he leaves a final message for his wife saying: I love you. It's sadly very sweet coming from a man who's been helping to reequip the major players of the Apocalypse.
Which makes his resurrection at the end of the book all the sweeter. Gosh, but it was good to see him alive.
When Satan is about to burst through the crust of the earth, we have this lovely scene:
Look very carefully at the difference in phrasing. In Aziraphale’s phrase, the ‘deep down inside’ comes before ‘that’ and makes no sense if it’s referring to the spark of goodness, as in a spark of goodness deep down inside Crowley. If it were, it should’ve been ‘I’ll have known that, deep down inside, there was a spark of goodness in you.’ The phrasing is correct in Crowley’s response (and it’s appropriate - Aziraphale’s bastard side really is pretty far down inside), but not in Aziraphale’s. Why? Maybe because he isn’t talking about Crowley. He’s talking about himself. That he has known all along, deep down inside, that Crowley had a spark of goodness in him. And it certainly looks in some parts of the book that he wants to believe in Crowley’s better side despite what he considers his better judgement - but formally he is still very much in the ‘demons evil, Heaven good’ camp for most of the book up till that point. Aziraphale is essentially apologizing for six thousand years of treating Crowley as inherently evil, assuring him that he did know better, deep inside, even if he didn’t always act like it. Setting things straight between them before their expected final battle. Getting the truth out there.
Aziraphale gave his flaming sword to Adam and Eve after they were cast out of Eden out of sympathy to them.
The way Crowley doesn't even hesitate to run into the burning bookshop to find Aziraphale.