Bridge to Terabithia
How we cite our quotes:
Terabithia was their secret, which was a good thing, for how could Jess have ever explained it to an outsider? Just walking down the hill toward the woods made something warm and liquid steal through his body. (4.139)
The act of going to Terabithia has the same physical effect on Jess that drawing does. Whenever he does either of them, he feels "something warm" ("peace" [2.11]) "steal through his body." Maybe it's the mental challenge or use of imagination that's having a physical, calming effect. Maybe his body recognizes something's good for him before his mind can. Either way, despite what other people might think or say, Jess can feel the rightness of going to Terabithia, of drawing, and of moving outside himself.
Jess tried going to Terabithia alone, but it was no good. It needed Leslie to make the magic. He was afraid he would destroy everything by trying to force the magic on his own, when it was plain that the magic was reluctant to come for him. (7.2)
Halfway through the book, Jess still relies on Leslie to get to Terabithia. He thinks both he and Terabithia "need" her "to make the magic," and isn't yet confident enough that he can do it himself. While he's opened up enough to the possibility of seeing Terabithia and sharing in Leslie's creation of it, he doesn't think he can shape it on his own. His transformation into being a magic-wielder is only partially complete.
Leslie's eyes were sparkling. "Arise" – she barely swallowed a giggle – "arise, king of Terabithia, and let us proceed into our kingdom." (9.47)
Like she's knighting someone, Leslie confers magic and kingship on Jess. They both believe in it, and yet recognize the silliness too. When Leslie tells Jess he's the king, he becomes transformed into that king.