Final answer:
Campbell uses the concept of 'smouldering' to create an image of passive and suppressed intensity in the poem.
Step-by-step explanation:
In the poem, Campbell develops the concept of 'smouldering' to create an image of passive and suppressed intensity in the poem. The speaker describes the 'smouldering' fires as 'ghostly' and 'unreal,' comparing them to 'half-shut eyes of wild beasts' and their victims in a den. This suggests that the purpose of using the concept of 'smouldering' is to convey a sense of hidden danger and destruction.