What effect does the ghost of Christmas past have on Scrooge?

Initially, Scrooge feels a strong desire to see the ghost put on its extinguisher cap. He "begged him to be covered." Something about the light is painful or, at least, uncomfortable for Scrooge and he "had a special desire to see the Spirit in his cap." Next, Scrooge wants to know why the spirit has come, interrupting his sleep, in the first place, and he scoffs when the Ghost says that concern for Scrooge's welfare...

Initially, Scrooge feels a strong desire to see the ghost put on its extinguisher cap. He "begged him to be covered." Something about the light is painful or, at least, uncomfortable for Scrooge and he "had a special desire to see the Spirit in his cap." Next, Scrooge wants to know why the spirit has come, interrupting his sleep, in the first place, and he scoffs when the Ghost says that concern for Scrooge's welfare is what brought him. 

Almost immediately, when the spirit removes Scrooge from the present and takes him into the past, Scrooge becomes aware of smells that bring back all kinds of memories. The Ghost sees that the old man's "'lip is trembling'" and he asks about a tear on Scrooge's cheek.   Then, when Scrooge is reminded of the fact that he spent his holidays alone, neglected by friends and family, "he sobbed."

When Scrooge sees the shadows of his lonely childhood, he "wept to see his poor forgotten self as he used to be." His weeping continues until he is reminded of the books he used to read and the characters with which he used to populate his imaginative world. Later, he cries again over his poor childhood and remembers the "'boy singing a Christmas Carol at [his] door last night'" and he now feels that he "'should like to have given him something.'" It is clear that, even at this early stage, Scrooge's goodness is being rekindled by the Ghost of Christmas Past. He still has a long way to go before he will be totally reclaimed, but his regret about how he treated the young boy at his door, as well as his copious and sincere tears, shows that he's begun to change already.