Here's the full excerpt containing the lines you quoted:
> And on his homeward journey he met a blooming Hawk
> Pulling out feathers said Now you blighter walk
These lines are part of a longer passage describing the tiger's journey after being created by the creator. The lines you quoted are spoken by the hawk, who is mocking the tiger for his lack of feathers.
While the lines are not directly related to the main theme of the poem (the nature of creation and the beauty and terror of the tiger), they add a playful and ironic twist to the narrative.