13:4 This day came ye out in the month Abib.
13:13 And every firstling of an ass thou shalt redeem with a lamb; and if thou wilt not redeem it, then thou shalt break his neck: and all the firstborn of man among thy children shalt thou redeem.
First month, i.e. April.
13:17 And it came to pass, when Pharaoh had let the people go, that God led them not through the way of the land of the Philistines, although that was near; for God said, Lest peradventure the people repent when they see war, and they return to Egypt:
The redemption of firstlings made a memorial sign to Israel of their own redemption.
(See Scofield "Zechariah 8:14") .