The stave opens with an exclamation of "Yes!" This immediately shows the change in Scrooge. Before his encounter with the ghosts, Scrooge was the man of "no," ready to slam the door in the face of the entire world. Over night he has gone from angry pessimist to exuberant optimist, embracing life.
In the next line, "best" and "happiest" set the tone for Scrooge's newfound, joyous mood. Further, to reinforce all of this, Dickens has Scrooge speak out loud and say
“I will live in the Past, the Present, and the Future!” Scrooge repeated, as he scrambled out of bed. “The Spirits of all Three shall strive within me."
Another literary device Scrooge uses in the passage above is alliteration, which is when the same first letter at the beginning of a word is repeated. Here, alliteration helps us to focus on "scramble" and "strive," which are both active words that emphasize Scrooge's determination to work to change his life.
Dickens then uses similes to characterize Scrooge's newfound spirit:
“I am as light as a feather, I am as happy as an angel, I am as merry as a schoolboy. I am as giddy as a drunken man."
Similes are comparisons using the words like or as. Scrooge is so joyful that his similes overflow: he can't stop at just one. And the similes he uses, such as "light as a feather," are a contrast to the Scrooge, who the night before was forging a heavy chain for himself—just like his friend Marley. Scrooge the night before was also grouchy, angry, and resentful of the holidays, anything but merry and giddy.
Scrooge then returns to the repeated exclamations:
"A merry Christmas to everybody! A happy New Year to all the world. Hallo here! Whoop! Hallo!”
It's a testimony to Dickens's skills as a writer that he is able to sustain this tone of joy throughout the stave by using positive, high energy words like "running" and "laughter," joyful dialogue, and many, many exclamation points to drive home Scrooge's transformation.