What are the motifs in To His Excellency General Washington by Phillis Wheatley?

Divine Right is a recurring idea in this poem. Students of this poem often focus on it as the work of the first woman of African descent to have her writing published in North America, but the only race that the poem itself mentions is "freedom's heaven-defended race." Just how the American people came to claim such an exalted title is not explained: instead, the poem just assumes that America is blessed, and uses that as evidence of George Washington's greatness.