The ending just makes one want to be a better human being.
Scrooge's flashbacks with him and his sister. He clearly loved her and the feeling was mutual. Unfortunately, her Death by Childbirth has left a scar on his heart.
Also to Scrooge's flashbacks, the delight of Mr. Fezziwig's Christmas party. Showing a time when a young Scrooge had a chance to enjoy himself and be happy, serving under a Benevolent Boss and surrounded by friends.
Scrooge coming to the Cratchit family dinner and showing that he can be kind and generous to his fellow man.
"I will not allow this to happen any longer, which gives me no alternative... but to... raise your salary!" Different adaptations play around with just how into the game Scrooge is when he fakes out Cratchett into thinking he's going to fire him, but even when the audience is in the know that he's changed, you can't help but giggle when he completely floors his clerk with the great news!
From the George C Scott version:
Scrooge: Finally, if the offer to dine with you today is still in force, I accept! Janet Holywell (Fred's wife): You'll be more than welcome!
Also try to listen to the chorus of "The Crachit Family Christmas Song" in the Mr. Magoo version, when it starts "We'll...have...the...Lord's bright blessing," etc., without tearing up.
The Goodman Theater of Chicago does this show every year. The 2002 production featured a Ghost of Christmas Past as played by a deaf man. At the end, all the cast members sang and signed "We Wish You a Merry Christmas."
In Ms. Scrooge, Ebenita helps give food to a group of homeless people at the end, which is especially poignant since her backstory showed her father had tried to open a grocery store before he died.
The last paragraphs (only portions are quoted, it's rather long):
Scrooge was better than his word. He did it all, and infinitely more; and to Tiny Tim, who did NOT die, he was a second father. He became as good a friend, as good a master, and as good a man, as the good old city knew...and it was always said of him, that he knew how to keep Christmas well, if any man alive possessed the knowledge. May that be truly said of us, and all of us! And so, as Tiny Tim observed, God bless Us, Every One!