A Sound Piece of Advice, Even if Your Sword Is Sheathed when You Wield It

I finally finished Moby Dick and wanted an easier read, so I've started the Narnia chronicle.  It is, indeed, easier; I read The Lion, the Witch, and the Wardrobe completely yesterday evening.

At the end of chapter twelve, Aslan instructs Peter, "And, whatever happens, never forget to wipe your sword."

What does it say about me that I could find a double entendre in classic, children's literature?