Final answer:
The theme of Phillis Wheatley's poem is that redemption and spiritual salvation are available to all individuals, regardless of race, and it calls into question the moral foundations of slavery.
Step-by-step explanation:
One theme of Phillis Wheatley's "On Being Brought From Africa to America" is that people of all colors can be redeemed by God. The poem challenges the prevailing view of African people during the 18th century and confronts the racist notion that blacks, being 'diabolic' in color, are spiritually and morally inferior. It refutes this by stating that even those seen as 'black as Cain' may be 'refin'd, and join th' angelic train,' suggesting that spiritual salvation and moral refinement are available to all, regardless of skin color. Wheatley uses her faith and the Christian doctrine, which was often used to oppress her people, as a subversive tool to claim equal spiritual worthiness and to call into question the ideologies supporting slavery.