"The Silver Doe" in Harry Potter.
I have always thought Harry's reaction to Snapes Doe patronus is meant to mean two things.
One. Snapes Patronus took form of Lily's. Everything Lily stands for, his Patronus is. Harry felt that deep sense of comfort and familiarity because it was his mum's whole essence. This was the closest Harry had ever been to actually having her there with him ever since her death.
Two. Snape spent his whole life after Hogwarts protecting Harry. And although he doesn't show it, and likely doesn't fully realise it, he cares about Harry in his own way. His patronus is, at its core, a representation of that. Harry felt that comfort because Snape was Harry's "protector" of sorts. When you meet the incorporeal embodiment of something who's whole goal is to keep you safe, you will likely feel overcome with a deep sense of reassurance and peacefulness.
Anyway. I adore this chapter. Probably one of my favourite chapters in the whole franchise. Harry describes the doe so elegantly