The main theme of the book "A Christmas Carol" by Charles Dickens is the power of redemption and the transformative nature of love, kindness, and compassion. The story follows the journey of Ebenezer Scrooge, a bitter and miserly old man, as he is visited by the ghosts of Christmas past, present, and future. Through these encounters, Scrooge is forced to confront the consequences of his selfish actions and the impact they have on those around him. Ultimately, the book encourages readers to reflect on their own lives and the choices they make, highlighting the importance of empathy, generosity, and forgiveness.