Final answer:
Frederick Douglass used adjectives to depict his mistress's transformation from kind and tender-hearted to cold and fierce, illustrating the corrupting nature of slavery on slaveholders.
Step-by-step explanation:
The overall effect of Douglass's choice of adjectives in his description of his mistress is a. to draw a stark contrast between her nature before and after her exposure to the institution of slavery. Douglass's narrative explicitly compares the initial warmth and kindness of his mistress to the coldness and fierceness she developed after becoming a slaveholder, showing a transformation from 'pious, warm, and tender-hearted' to one with a 'stone' heart and 'tiger-like fierceness.'
Through his poignant and vivid language, Douglass's storytelling highlights the dehumanizing effects of slavery not only on the enslaved but also on those who enforce and live by its brutal codes. His detailed account skillfully illustrates how his mistress, who initially did not fully grasp her role in the underlying system, eventually succumbs to the roles and expectations foisted upon her, leading her to cease her kind treatment of Douglass and adopt an attitude similar to her husband's.
This transformation serves to underline how slavery corrupts even those with the 'finest feelings,' as it violently opposes the very essence of humanity and compassion, which she initially displayed.