What is the central theme of the BFG?

The central theme of The BFG is teamwork.
The Big Friendly Giant has lived amongst other giants his whole life. Unlike the other giants, he is extremely against eating human beings. Instead of eating humans, he spends his time collecting dreams and blowing them into children's bedrooms with his trumpet. Due to his beliefs, he does not get along with the other giants. The other giants, such as Fleshlumpeater and Bloodbottler, are constantly teasing him and throwing him around.
When Sophie spots the BFG blowing dreams into other children's windows, he snatches her from the bedroom, because he fears that she will tell everyone that giants are real.
As they begin to talk about their lives, Sophie and the BFG discover that they are both lonely. Sophie grew up in an orphanage with no family or friends, and the BFG doesn't get along with his own kind.
When the BFG and Sophie were on their own, they felt lonely and weren't able to accomplish a lot. Before Sophie came along, the BFG didn't know there was a way to defeat the giants. However, together they are able to formulate a plan to defeat the giants that have threatened the world for so long. The BFG is able to use his hobby of dream collecting, and Sophie is able to use the fact that she is a human in order to accomplish their plan. In the end, they are successful in convincing the Queen of England to help them and are finally able to defeat the giants once and for all. They would not have been able to follow through with the plan without each other.