What does the Law of Interaction says about?

In Phillis Wheatley's poem "On Being Brought from Africa to America", she uses a unique argumentative style for elaborating her point of view. She states rhetorical and characteristic logic based on enlightenment.  

In the first line of the iambic parameter, she uses words like "mercy" and "pagan" to stress that God shows gracious gestures towards his people but his people are very indifferent. They show no mercy but act like demi-gods.

She emphasizes on racism and American slavery. She also describes Christianity is the only way to salvation.

The rhyming scheme of this poem is AABBCCDD.