| This is one of my favorite poems of Dylan Thomas, both through its incredible use of language to aurally project the atmosphere it is trying to create and its wonderful theme. The poem is about life and death, the process that brings about both, and how these two natural forces are not actually two, but one.
Much of this feeling of oneness is created by juxtaposing the two together in one image:
"Drives my green age..."
"Stirs the quicksand; that ropes the blowing wind..."
"The force that drives the water through the rocks..."
"How of my clay is made the hangman's lime..."
All of these are images of life and death combined into one; green, blowing wind (the breath of life), clay, and water as symbols for life... age, quicksand, lime (used to accelerate decomposition of publically hanged men in their graves), and rocks as symbols for death. By joining them into one coherant image, the merging of the two becomes more apparent.
Dylan Thomas also brings about this unity through the one constant in the poem, the driving force. All else is a swirl of conflicting images and confusion, what anchors the poem is the one force that serves to fuel it all. This force cannot create both life and death unless it is both life and death, rolled into one package.
All that makes the difference is time. Everything changes, the one force brings the joy of life and the despair of death in cycles. They are not opposing gods, waging an eternal battle for the state of the world. They are one, they feed each other. Death becomes life becomes death becomes life.
And I am dumb to tell a weather's wind
How time has ticked a heaven round the stars. | 
