The Ghost of Christmas Past leads Scrooge to reach certain conclusions by making calculated comments that force him to reflect on his recent behavior and compare it to his past
Scrooge tries to extinguish the Ghost's light

But cannot hide the light, showing that good will prevail and Scrooge will be redeemed
The Ghost of Christmas Past shows Scrooge's past to help him understand why he is the way he is and empathize with him, making his redemption more plausible
Dickens is trying to make the point that Scrooge has to reflect on his past to understand his present, and the same applies to the readers
