“Up-Hill” by Christina Rossetti can be seen as an allegory on the journey of life or, more specifically, on the spiritual journey of the soul—the Christian soul, to be more precise. Rossetti makes it clear that this journey is long and hard, with many challenges along the way.
The road winds “up-hill all the way” and will take a whole day's journey. Here, a whole day stands for an entire lifetime. There can be no doubt that Rossetti wishes to convey the impression that a life's journey, or the journey of the Christian soul, is not supposed to be easy.
To be sure, rest can be found from the rigors of the journey, but only in death. Entering eternity at the end of our lives is represented in the poem by the metaphor of the inn, where the individual soul shall find rest, along with all the other souls who've previously made the journey. There is ample room at the inn for all who make the trek, perhaps an allusion to the words of Jesus in John 14:2, which Rossetti would have known very well:
In my Father's house are many mansions.... I go to prepare a place for you. (KJV).
This is the ultimate destination for the Christian believer, one who has faithfully followed the long, winding road of life while remaining on the path of righteousness.