In A Nutshell
This whole poem is nonsense.
No, it's true. "Jabberwocky" is, in all probability, the most famous nonsense poem ever written in English. The vast majority of the words in this poem are clever inventions of its author. This makes sense if you consider the fact that it was originally published in its entirety in the 1871 book Through the Looking-Glass, and what Alice Found There by Lewis Carroll. Does that sound familiar? It should. With its companion piece, Alice's Adventures in Wonderland, "Jabberwocky" is the basis for the wildly popular Disney movie Alice in Wonderland.
The poem itself was originally just the first stanza, and was published in a magazine that Carroll put together for family and friends. He entitled that first stanza "Stanza of Anglo-Saxon Poetry." Here Carroll was decidedly tongue-in-cheek, given that he was not Anglo-Saxon. ("Anglo-Saxon refers to people who lived in England in approximately 600 A.D.).
Carroll was English, however, and so we tend to think that "Jabberwocky" was influenced both by that Anglo-Saxon verse which he parodies (killing things with swords, heroes on quests, etc.), as well as a few local English legends (the north-English myth of the Lambton Worm is plausible here – it's about a hero that goes and vanquishes a livestock-eating slithery thing). In other words, "Jabberwocky" is part of a larger children's story gone sort-of awry. The nonsense and the rhyming and the fantasy characters all pin this poem down as something your mom or dad might have read you when you were five, but it's much more than that.
Critics have been raving about Carroll for decades. They just love the way that he manages to make his fantastical stories work on both a child's and an adult's level. His stories and poems are funny and whimsical, but they're also complicated, dark, and bitter. Children are entertained by the whimsy and fantasy. As adults, we see these layers of complexity emerge the more we read the work. "Jabberwocky" and the Alice stories were wildly popular in their time, and they're wildly popular now – for good reason.
Carroll's real name, by the way, was Charles Lutwidge Dodgson, and in addition to being one of the greatest and most popular storytellers of his time, he was also an accomplished mathematician, logician, deacon, and photographer. And you thought your schedule was packed.
Why Should I Care?
Maybe it's hard to see why anyone should care about a poem that is, in essence, a bunch of nonsense words strung together in verse. After all, it's not like we ever use made-up words, or make noises when we react to things, or enjoy tales of violent heroism? Right? Right?
So maybe your use of the word "gaaah" on the internet doesn't have anything to do with Lewis Carroll, but what about, say, your love for a good, simple story of good vs. evil? "Jabberwocky," despite its goofy language, is about facing your demons. It's a strange world we live in, filled with all sorts of unknowns, and every now and again you're bound to round a corner and come face to face with something horrible (metaphorically, we hope). But we all have "vorpal blades" (18) lying around somewhere, just waiting to vanquish our awful foe. And when we do, it's awesome. We're awesome. And we go along our merry way.
By presenting in whimsical tones a triumphant tale of conquest, Carroll tells us that not only does good win out in the end, but that it will win out even if we're not taking things deadly seriously all the time. And that's refreshing, isn't it?