"Beware the Jabberwock, my son (5)
This is the first instance in the poem where we have any notion of gender at all – "my son." It's also the introduction of humans into the piece. Up until this point we've just had the very strange opening quatrain, which involves a lot of unfathomable things wandering around in the woods. So our first encounter with humans is this advice-session between a father and his son. It's a little like the "the real world is a dangerous place" talk you might have gotten from one of your parents at some point in your life. In an adventure tale, it's practically a rite of passage – "All right son, you're going to be facing some big bad things out there, so buck up and be brave!"
He took his vorpal sword in hand; Long time the manxome foe he sought– (9-10)
Our hero sets out right after he gets the warning from his father. This kind of response is typical of adventure sagas and epics. Think Beowulf. Or Lancelot and the Copper Knight. Or any fairy tale involving princes and dragons. Or Lord of the Rings. And then, when he can't find the Jabberwock right off the bat, he's so focused on defeating it that he just keeps looking, sword at the ready. Again, if we think of this piece as a kind of fairy tale, it makes sense.
He left it dead, and with its head He went galumphing back. (19-20)
There's the element of trophy in this quote. The protagonist here is kind of like a modern hunter who has antlers or even whole animal heads mounted on the wall. The protagonist could go home with a bloody sword and have that be that, but it's probably way more satisfying to the parent if he comes back bearing the gory evidence that yes indeed, the Jabberwocky is no more.