Final answer:
Line 20 is pivotal in comparing the gentle lamb and the fierce tiger, emphasizing the complex nature of the creator and evoking moral and philosophical contemplations on creation and the dualities within nature and humanity.
Step-by-step explanation:
Line 20 of the poem plays a crucial role in developing its thematic concerns. It juxtaposes the innocent and gentle lamb with the fierce and powerful tiger, revealing the complex nature of the creator who could forge both. This contrast offers insights into the moral and philosophical questions that the poem raises, especially regarding the nature of good and evil, creation, and the inscrutable motives of the creator.
In examining the thematic development framed by this line, the powerful imagery of the tiger and the references to the lamb underscore the fierceness and the innocence of these creatures. This contrast can be interpreted as a reflection on the dichotomy within the natural world and possibly within the human condition, suggesting a depth to the creator's design that is beyond easy comprehension.