I think my favourite moment of the film (it's hard to pick) is nearing the end, when George Bailey is running down the main street of Bedford Falls
so full of joy he is unable to contain it, shouting "Merry Christmas!" to everyone he sees. It's such a cathartic moment; we've just seen George at his lowest point- broken, defeated and, having been mockingly told by Mr. Potter that he's worth more dead than alive, contemplating suicide. Then, as Clarence shows him what his town- and the people in it- would have been like without his influence, we've seen George's confusion, anger, and ultimately fear that he's lost everything truly important: his family and friends. In the end, George returns to his life and nothing has changed: the money is still missing, his car is still crashed, Mr. Potter is still trying to destroy him. But George has changed and realised that his life with all its disappointments and pain is nevertheless a wonderful one, and he's filled with a euphoric joy which spills out as he runs home to be with his family.