Never Judge a Person by Looks

I think the theme is never judge someone
based on their looks. This is because when Sophie got taken she thought the BFG was a
bad giant wanting to eat her for dinner."'What type of human beans do you eat?' Sophie asked. 'Me gobbling up human beans!? Never! Other giants, yes..I is the big friendly giant.'" Here Sophie then sees how different the BFG is
from the other giants.