It is a scene from "The Lion, The Witch, and The Wardrobe" where the children are hearing for the first time of Aslan the Lion, the allegorical Christ figure of the book:
"Ooh!" said Susan, "I'd thougth he was a man. Is he--quite safe? I shall feel rather nervous about meeting a lion."
"That you will, dearie, and no mistake," said Mrs. Beaver, "if there's anyone who can appear before Aslan without their knees knocking, they're either braver than most or else silly."
"Then he isn't safe?" said Lucy.
"Safe?" said Mr. Beaver. "Don't you hear what Mrs. Beaver tells you? Who said anything about safe? 'Course he isn't safe. But he's good. He's the King, I tell you."