According to Jewish literature, Isaac, the only son of Abraham and Sarah, was born on the first day of Passover and "at his birth the sun shone with unparalleled splendor, the like of which will only be seen at the time of the Messiah's coming. The suggestion here is that the birth of Isaac was a prototype of the coming of the Messiah. [John C. Lefgren, April Sixth, p. 25]