Final answer:
Firstborns fast on erev Pesach as a remembrance of the tenth plague during the Exodus, where the Angel of Death passed over the homes of the Israelites, sparing their firstborns.
Step-by-step explanation:
Firstborns are required to fast on erev Pesach, or the eve of Passover, as a commemoration of the tenth plague that struck Egypt. This biblical event led to the liberation of the Israelites from slavery.
According to the book of Exodus, the Angel of Death passed over the homes of the Hebrews that were marked with lamb's blood, sparing their firstborns while taking those of the Egyptians.
This solemn fast is observed by the firstborns as a sign of gratitude for their ancestors' salvation and to reflect on the significance of freedom and survival.
The story of Passover is retold during the seder, a ritual meal that marks the beginning of the holiday, where questions are asked and answered to remember the Israelites' journey from slavery to freedom.
The fast undertaken by firstborns on erev Pesach serves as a physical reminder of the hardships endured by their ancestors and the mercy they received.