Final answer:
The poet demonstrates the theme of good and evil in the poem through the spiritual destitution of the man and his contemplation of wicked deeds.
Step-by-step explanation:
The poet demonstrates the pervasive theme of good and evil throughout the poem by depicting the spiritual destitution of the man. The existence of poverty creates a gap between the shepherd and his children, leading him to contemplate wicked deeds. The poet uses the shepherd's thoughts and actions to exemplify the presence of evil.