What is "characterization"? How does characterization add to the reader's understanding of the theme of the story?
Characterization is the process of revealing the personality of the character.
By giving details on a character's personality, the author helps readers understand that character more accurately. By showing how they respond to different situations, the author gives glimpse of their view on different topics.
In dynamic characters (characters that go through some sort of change in the story), these details and responses change from beginning to end. If the reader can interpret whether or not these changes are being portrayed as positive, then the theme is not far off.
Let's say that Jerry is a jerk at the beginning of the story, but at the end he is a kind and forgiving young man because someone showed him how he makes others feel. The theme is probably "Treat others as you would like to be treated," or something similar (Assuming Jerry is the main character/protagonist).