Line 1

Celestial choir is the poet's muse, a device of neoclassicism. The muse is called on to inspire the poet's writing.

Line 2

"Columbia" was a term Wheatley used for America, later used by other writers.

Line 3

"Freedom's cause" is the central theme of the poem, the struggle of the colonists to be free from England, even if it meant going to war against the more powerful British.

Line 4

In this context, "dreadful" means "inspiring awe or reverence," "in refulgent arms" means "in brilliant defense." In this sense, Columbia (America) is portrayed in righteous terms for standing up against England.

Lines 5-6

The speaker of the poem points out that other countries are watching something unique occurring in the uprising. And as it turns out, the American Revolution directly inspired the French Revolution.

Lines 7-8

Heaven is affected by the struggle in a sorrowful way.

Lines 9-12

The poet...