The ending just makes one want to be a better human being.
Scrooge coming to the Cratchett family dinner and showing that he can be kind and generous to his fellow man.
From the 1951 version, Scrooge, starring Alastair Sim:
The scene where Scrooge visits nephew Fred's home on Christmas Day, worried that he's irreparably soured their opinion of him, only to find they are delighted to welcome him to their Christmas party.
Very, very effective - this formerly caustic, flinty man enters their home the picture of quiet humility to the housekeeper.
The entire scene of waking up Christmas morning.
The 2009 film also portrays this moment with the same heartwarming feeling. His nephew is a gentleman.
"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."