The French Revolution is the perfect setting to analyze the limits of justice and what happens when a ruling class continues to suppress the people. In doing so, Dickens explores important themes such as the destructive nature of revenge, revolution, the importance of sacrifice, and resurrection.
Juxtaposition is a literary term describing the placement of things near one another. The "things" could be people, places, ideas, objects, moods, motifs, emotions, etc.
It was the spring of hope, it was the winter of despair.
The passage is a run-on which is filled with contradictions. The winding length of the quote indicates a story and time from the past, and the contradictions exist at the same time, making the period in question paradoxical in nature.
The narrator is reflecting on a time that is tumultuous and full of tension because the aristocracy and the commoners are at odds with one another, much like the contradictions Dickens highlights in these opening lines.