"While freedom’s cause her anxious breast alarms,..."
See in text (Text of the Poem)
Wheatley constructs this line using an unusual syntax in order to draw a double meaning from the word “alarms.” The clause could logically be reassembled as “While freedom’s cause alarms her anxious breast.” In this case, “alarm” means to call to action, with “freedom’s cause” as the subject and “her anxious breast” as the object being roused. As it is written, however, “her anxious breast alarms” draws on another usage of “alarm,” which means to arm oneself. Thus, “her anxious breast” operates as both subject and object, arming itself. This second reading is not strictly accurate, but it is reinforced by the next line with its image of “refulgent arms.”