In "Jabberwocky," "Good vs. Evil" is linked with the theme of "Violence." When good (our hero) and evil (the Jabberwock) meet in this story, violence ensues. "Jabberwocky" pits the individual (one lone man) against a mythical beast. Since this beast doesn't exist in our world, it becomes something bigger, a kind of metaphor for Evil with a capital E. If it were simply human vs. human – say, white knight vs. black knight – you could draw the same conclusions, but perhaps the outcome would be less surprising. One small man triumphing over a big huge beast is an order of magnitude unto itself.
We fear, and often label as "evil," that with which we are unfamiliar.
Evil in "Jabberwocky" takes the form of a beast because it makes evil seem alien and inhuman.