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 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.