While the familiar rhythm of iambic quatrameter and the simple rhyme scheme of Frost's poem connotes relaxation, the repetition of the last line as the reminder that the poet has obligations, suggests his reluctance to go as well as the persistent interference of these obligations upon his enjoyment.
Frost is also a master of imagery. Even the title of this poem has pristine imagery. He is able to use language that appeals to all of the senses, not just sight. The reader can almost smell the horse, and hear the silent darkness.
He uses a lot of alliteration:
"watch his woods"
"He gives his harness..."
"sound's the sweep"
"dark and deep"
There is a longing for death (“frozen lake,” “darkest evening of the year,” “The woods are lovely, dark and deep” seem to support this view), but that is not what the poem is exclusively about. If there is a momentary longing for death in the poem, there is also the reassertion of the will to face the tasks of living.