One of the themes that emerges from Hughes' poem is the defense of one's dreams.  Hughes reaffirms this themes in a couple of critical moments in the poem.  The opening line of "Hold fast to dreams" helps to convey a condition in which individuals are reminded of the importance of clinging to visions of their subjectivity.  This can be seen in Macbeth.  Once Macbeth fully immerses himself in what he must do, he demonstrates holding "fast to dreams" throughout the drama. He never lets go.  His vision of a world that is appropriated in accordance to his own subjectivity is never surrendered.  Macbeth's commitment to his dreams is matched to how Hughes describes a world in which dreams are absent.  "Life is a barren field frozen with snow" is a descriptor of the emptiness and hollowness in a world where no dreams exist.  To this end, Macbeth drives his own existence in the belief that abdicating his dreams would result in such a vision. The theme of Hughes' poem is one in which individuals cannot sacrifice their ability to dream.  This is something that Macbeth, himself, embraces and never loses in the arc of his characterization.