The last two lines of this poem contain a repetition. Frost repeats the idea to emphasize the importance of carrying on the journey before the metaphorical sleeping. Besides, the last two lines present the idea of sleeping from two different perspectives. The first "sleep" is about to take a rest. While the later reference deals with death. The speaker has a long way to go before death and along the way, he cannot even waste a moment in lethargic thoughts.