Dramatic pauses are key here and in the poem. It's an inspiring call to action. You should definitely check out the audio recording of McKay reading the poem in his Jamaican accent. McKay used to write in his native dialect. Here is an example of a line from his poem "A Midnight Woman to the Bobby:" "Ko 'pon you' jam samplatta nose." The line comes out in standard English to mean something like, "Look at your flat, sandal nose." It just doesn't sound that good in standard English. Likewise, "If We Must Die" comes alive when it's read out loud.