In The Garden, we see a fall from a state of innocence and paradise. This doesn't mean that during the beginning, the narrator didn't experience negative emotion; of course he describes feeling a vast array of emotions, but the community was healthy, and he was a healthy part of it, enjoying relationships to many families, many of them Jewish. His innocence is lost when the Jews are deported to concentration camps and systematically executed, leaving him in a bizarre state of absolute horror.
That is why he fails his classes, after all. He can't focus on math and numbers. Notice that in the concentration camps, Jews were identified in mathematic ways; they were tattooed with numbers in place of their names, and they were herded in groups. Even today, it is easy to say, "six million," without remembering that each person in that group was a complete human being, with a soul. The narrator's aversion to math can be seen as a symbol for this problem. He can't focus on numbers when he is haunted by the memory of his real friends.
For the narrator, the historical truth of WWII and the Holocaust was woven into his identity, which is clear from his relationship to Micol. His unrequited love for Micol shows that she is an important part of his developing psychology; he is infatuated with her, and he longs for her with the full intensity of first love. He has to wonder whether he missed out on a chance to be with her by rejecting her invitation into her garden (again, the paradisal symbol). Instead of attaining love, he witnesses in horror as the possibility of love and union is removed from him by the horrors of torture and mass murder. His martyrdom shows that the cost of the Holocaust was that it damaged love and community in European towns.
