"Dreams" is a very straightforward encouragement to the reader to not give up when life becomes challenging. Hughes first compares the death of a dream with "a broken-winged bird that cannot fly." Just as the bird would be incapable of flight, a dream that has died will never be brought to fruition.
Next, Hughes encourages the reader to "hold fast to dreams" and to not allow them to escape or "go." Life without dreams, he explains, is as cold and desolate as "a barren field frozen with snow."
The theme of the poem lies in its instructions to the reader to hold fast to dreams and to keep striving to make them happen, regardless of obstacles or complications along the way.