Supernatural has finally come to an end, after an incredible fifteen seasons of monster-hunting and god-fighting, and it was an incredible run. In the end, Sam and Dean Winchester defeated the biggest bad of all - God - and found their way to Heaven (and this time, there's no coming back). Fans watched these two grow from relatively naive and new hunters to apocalypse-stopping near-immortals, who cheated Death, God, the Devil, and more.
But with a decade a half between the first episode and the last, how many fans can remember how the Winchesters, and their friends, first appeared on the small screen? From the very first words they spoke to the last, these show quite how far the main characters in the series have come.
Chuck
Sam and Dean approached the run-down... approached the ramshackle house with trepidation - Guys wait, wait wait wait, please wait, guys!
When Chuck first appears, it is as Carver Edlund, the writer of the 'Supernatural' novels that shock Sam and Dean (unsurprisingly, given that the books are the story of their lives). His opening line comes as he is typing up the next Supernatural book, narrating it out loud to himself. Later, it appears that Carver, aka Chuck Shirley, is a Prophet, which would explain his knowledge, and finally, the Winchesters discover that he is actually God himself. His final lines, especially in contrast to his first, show how far he has fallen. From being totally in control, he has reached the point of being powerless, on his knees and begging for them to come back.
Mary Winchester
Come on, let's say goodnight to your brother - Jack, please, listen to me.
Mary Winchester has a wild ride on the show, as she is killed off at the very beginning (via demon), and then returns thanks to flashbacks, time travel, alternate universes, and eventually resurrection, before being accidentally killed by Jack in the end. Both her first and last lines paint her as a mother, though, and that's what she always was. First, it's to her boys when they were little, and in the end, it was to Jack, as she was trying to be a mother to him, too.
Rowena
This is Raul's girl, isn't it? Clever name, by the way - Thank you, my dove
Rowena became a fairly major player in the Supernatural world, but her opening lines don't really have much to do with anything. It's the kind of opening speech that any number of freak-of-the-week would have, as she has an opening scene that shows off her powers.
Her final line, though shows how much she has changed - and how she has softened (while still becoming Queen of Hell, of course), and learned to show how much she cares.
Jack
Father? - Goodbye.
Jack's first and last lines are short and sweet, and could really sum up his entire arc on the show. Jack was only around for the final few seasons, the Nephilim who started off worrying everyone (who thought he might end the world), and who ended up saving everyone, stripping Chuck's powers and essentially taking up the mantle of God. It's noteworthy that his first line is a question, and he spends most of his arc questioning himself and his place in the world. In the end, though, he is done with questions, and has found where he is meant to be.
Lucifer
It's you, Nick. You're special, you're chosen. - You don't learn.
Lucifer, despite being a huge character for most of the show (and a fan-favorite) doesn't really have much depth to his first and last lines. Initially, he is attempting to lure his vessel into letting him possess them, which is a useful set up for the character (and how manipulative he can be) but doesn't jump out as an opener.
His final line, too, makes perfect sense in the scene, but doesn't really illustrate any major changes. Then again, Lucifer arguably has less growth than any other main character (which isn't a bad thing, per se), so perhaps this is why his opening and closing lines don't have so much of an impact.
Crowley
Mr Pendleton, I presume - Bye, boys.
Start to finish, Crowley is a charmer, a smooth talker, and approaches everything with style. He also goes through a lot in the show, from a more straightforward villain to a character willing to die to try and save the world. His opening line doesn't do much but set up his distinctive way of speaking, but his last line is perfect. Crowley is known for his 'hello, boys' greeting whenever he sees the Winchesters, so 'bye, boys' is a reference to that, and also places the Winchesters (and his relationship to them) front and center in the end.
Bobby
here you go - So I guess the question is, what are you gonna do, Dean
Sometimes, an opening line just can't be anything special, and Bobby's 'here you go' definitely falls into that category. However, his final line is, like Crowley's, perfect. Spoken to Dean while in Heaven, it sums up their relationship - Bobby giving heartfelt and straightforward advice, and helping to guide Dean on his path, just like he always has.
Castiel
I'm the one who gripped you tight and raised you from perdition - Goodbye, Dean
Both Castiel's first and last lines are to Dean, which is absolutely perfect for the character, who ended his time on the show confessing that he has always been in love with Dean (before dying to save him). Of course, in his first appearance, he was much colder, more intimidating, and even frightening, whereas his last saw him (and the fans) in tears as he said goodbye. These lines show how central Dean is to Cas, and how he has softened and become more human as time goes on.
Sam
Do I have to? - Dean
Of course, Dean is also central to Sam's life, and his short-and-sweet first and last lines show that. His first line may be less than thrilled, but that fits the character. Sam spent most of his life struggling with the idea of being a hunter, and wanted, over and over, to find a 'normal' life away from it all. 'Do I have to?' is a fantastic way to show that from the start. And he does get that (to an extent) in the end- but no matter what, he finds his way back to his brother in the very end.
Dean
Night, Sam - Hey, Sammy
And finally, Dean - whose first and last lines are almost exactly the same: addressing his brother. Throughout the show, Dean's defining factor has been his role as big brother, and how he views his family and Sam as the most important thing in the world. There is nothing he wouldn't do for Sammy, and so it shouldn't be surprising that from start to finish, these are the most important words that come out of his mouth.