Rise up, rise up,
And, as the trumpet blowing
Chases the dreams of men,
As the dawn glowing
The repeated imperative opens the poem. It has biblical overtones; a call to arms that extends back into history. The repetition adds to its urgency. 
 There are any number of commands of this nature in the Bible. An example may be  Judges 5:12 , with the command “Awake, awake, Deborah. Awake”. In this case it was a call to a female prophet and warrier to free her people.  During the First World War the call was to rise up against a perceived threat of German expansionism.
The Trumpet