Symbolism, Imagery, Allegory
The BFG begins during the Witching Hour, a time in the middle of the night when humans are supposed to be asleep. That’s the time when “all the dark things came out from hiding and had the world to themselves.” (1.9)
That makes Sophie sort of a trespasser, peeking outside during a time that’s not supposed to belong to her. That’s how she catches sight of the BFG blowing a dream into the bedroom window of the children across the street.
From the moment you open The BFG, sleep and dreams are front and center. From then on, they’re everywhere. Like cell phones, but more natural (although the BFG can create them by putting a trumpet by people’s ears). Plus, even when Sophie and the BFG are talking about other things, the BFG’s bottles of dreams are in the scene, sitting on the shelves surrounding them.
Also, sleep separates the giant world from the human world. Giants catch their z’s for only a couple hours a day, but (as you may know) it’s different for humans. The BFG points out:
“The human bean who says he is fifty has been fast asleep for twenty years and is not even knowing where he is! Not even doing anything! Not even thinking!” (13.3)
Something we spend that much time on must be important, after all.
Human sleep gives giants their power over humans. It allows the people-eating giants to easily catch humans and gobble them up without being spotted. And it allows the BFG to do something nice for humans by giving them dreams.
Onto the symbol part. Out of all the powers Roald Dahl could have given the BFG, why did he choose the power to catch good dreams and grant them to other people?
Dreams are unexplainable. The BFG tries to tell Sophie as much:
“It’s all a bit beyond me,” Sophie said.
“Dreams is full of mystery and magic,” the BFG said. “Do not try to understand them.” (16.17-18)
See how he uses the word “magic” to describe them? The BFG keeps trying to tell Sophie that there’s so much more to the world than what she can see. Dreams are another reminder of the world’s many mysteries. And the BFG’s knowledge about the unexplainable phenomenon makes him something more than giant who spouts silly words: it makes him seem wise. In a hippie, earth-mother sort of way.
In the end, Sophie and the BFG take back the giants’ power by capturing them in their sleep. Now that’s karma.