Fasting always appears in situations of real or threatened loss. Sometimes the loss concerned is final, as when fasting appears in mourning the dead. At other times, fasting occurs in close proximity to prayer, and it seems to aid in reversing an evil decree. How the same rite can appear in both contexts, be both efficacious and not, requires some thought. Perplexity regarding the meaning of fasting also follows from another angle. Formative Judaism
Volume 2, Page 432