"And hast thou slain the Jabberwock? Come to my arms, my beamish boy! O frabjous day! Callooh! Callay!" He chortled in his joy. (21-24)
We've covered the whole middle bit of the poem. As expected, when the hero comes back bearing the severed head of the Jabberwock, the father is unable to contain his joy. This is a traditional, idealized father-son relationship. The son has shown his bravery and therefore his masculinity to his father by killing something evil, and then bringing back the proof. For the father in the poem, this is about the best thing he could wish for (as evidenced by all the exclamations). His son has proven himself in battle, which makes him wiser, more experienced, and, well, more manly in the scope of this poem.