Exodus 13:14

And it shall be when thy son asketh thee in time to come
Or "on the morrow" ^F8, the day following such a separation of the firstborn of clean creatures, or such a redemption of the firstborn of unclean ones, and of man, or in any later time: saying, what is this?
what is the meaning of this? for what reason are such things done? that thou shall say unto him, by strength of hand the Lord brought us
out of Egypt from the house of bondage:
by laying his mighty hand upon the firstborn of Egypt, and destroying them, which made the king of Egypt, and his people, willing to let Israel go; (See Gill on Exodus 13:3).