Lewis establishes the Witch as a Satan-like figure. According to Christian belief, before the suffering, death, and resurrection of Christ, human souls were automatically forfeit to Satan after death. This state of affairs was due to Adam's original sin in the Garden of Eden, when Adam disobeyed God's order not to eat the fruit of the Tree of Knowledge. God gives human beings free will, knowing that they may choose to sin. Because God is merciful, He sends Christ to redeem humankind after Adam's fall. But because God is just, someone has to die for the sins of human beings if humankind is to be redeemed, and this is what Christ takes upon himself to do. Similarly, in The Lion, the Witch, and the Wardrobe, Aslan cannot fight the law that traitors must forfeit their lives to the witch, but he can sacrifice himself in Edmund's place. Aslan's sacrifice must be what Aslan and the Witch discuss.
Lewis does not explain exactly what Aslan and the Witch talk about in their secret conversation. Instead, Lewis builds anticipation, describing only the reaction of Aslan and the Witch to their agreement. We are curious why Aslan is crestfallen and unhappy. We also realize that he must love Edmund intensely for him to make such a sacrifice to save his life. If we read the text very closely with an eye for other Christian symbols, we can predict what will happen next. Lewis is deliberately vague in creating connections to the Christian religion, allowing him to prolong the suspense and anticipation. Aslan's final roar is a release of tension, and the first time that we ever see him express powerful emotion. He usually appears dignified and reserved. Aslan's strong reaction to the Witch's question demonstrates that only an evil character like the Witch would dare doubt the lion's veracity. Aslan's roar also signals his great frustration and anger at dealing with forces that are out of his control.