Answer:In this passage, Stowe is discussing the passage of time. His point -- and the lesson he is trying to teach -- meshes nicely with the technique he uses to get this point across.
Stowe makes the point that when looking back on bad times ("looking back to seasons which in review appear to us as those of deprivation and trial") we often remember that there were moments of happiness ("diversions and alleviations") that prevent us from being totally unhappy.
Stowe is also trying to indicate that time passes almost without our being aware of it. While it is true time passes "a day at a time," days accumulate without our being aware of it. And so, the year will end when it feels it has barely begun. The time jump Stowe uses is a perfect way to illustrate this point.
Although Tom has to live one day at a time, and even though he is not entirely happy, before he knows it "two years were gone." Thus, this time jump allows Stowe to do two things.
First, this time jump has a practical application. This drastic time jump of two years allows Stowe to fast forward quickly in time without describing all the little and unimportant events that happened over the course of two years. (It is enough to know that Tom lived through times of deprivation but had moments of happiness.) Second, this time jump allows Stowe to illustrate the theme of the passage of time that he is discussing in this excerpt.
Explanation:
