The theme of Robert Frost's poem is the destuctive potential of hatred and desire.
In his poem, Frost explores with amazingly eloquent brevity two forces which have the potential to bring destruction to the world. The first of these two is desire, which Frost likens in heat and intensity to fire. The second of the two is hatred, which he likens to ice.
In the poem, Frost examines the question of which of these two elements will ultimately destroy the world. Although he notes that there are avid supporters of both possiblities, the poet himself believes that, in the end, it will be fire, or desire, which will do the job. He closes the poem with an acknowledgement also that, although he did not choose it as being the likely cause of the earth's demise, hatred, or ice, has an equal potential to bring about final destruction.
Since ancient times literature has been the catharsis of the world, that is the way of purification. The end is a motif in this poem but the ways in which it should come are a synthesis of the poet's vast knowledge of cultures and especially religious writings of various origins. The end may come in different ways, but the theme is purity, return to innocence, appreciation of the basic human values. It is not desired by superior forces that we ,humans , to be ended , extinguished from the earth, but a purification is needed in order than humanity to continue existing as real , not in a state of degradation, which anyway, leads to nowhere!The theme is the sanctity of the human soul.