From “the first seven years” by bernard malamud feld had a sudden insight. in some devious way, with his books and commentary, sobel had given miriam to understand that he loved her. the shoemaker felt a terrible anger at him for his deceit. why is this excerpt an example of an epiphany?

Epiphany is defined as a sudden moment of realization, finally understanding something which has been elusive for a very long time. In the excerpt above, it says that 'Feld had a sudden insight.' That insight is his epiphany - he finally came to terms with something which he wasn't aware of before.
Epiphany is a common tool used in literature - it was often used by writers such as James Joyce. 

Isaw that onlinemade me laugh