The practice of setting apart the firstborn and paying redemption money was to be a lasting ordinance in Israel. The first instruction, about this, and its reason, is found here:
Ex 13:1, 2, 14-16 - Then the LORD said to Moses, “Consecrate to Me
every firstborn male, a The firstborn from every womb among the
Israelites belongs to Me, both of man and beast.” … In the future,
when your son asks you, ‘What does this mean?’ you are to tell him,
‘With a mighty hand the LORD brought us out of Egypt, out of the house
of slavery. And when Pharaoh stubbornly refused to let us go, the LORD
killed every firstborn in the land of Egypt, both of man and beast.
This is why I sacrifice to the LORD the firstborn male of every womb,
but I redeem all the firstborn of my sons.’ So it shall serve as a
sign on your hand and a symbol on your forehead, for with a mighty
hand the LORD brought us out of Egypt.”
But the instruction is repeated in other places:
Ex 22:29, 30 - "You shall not delay the offering from your harvest and
your vintage. The firstborn of your sons you shall give to Me. "You
shall do the same with your oxen and with your sheep. It shall be with
its mother seven days; on the eighth day you shall give it to Me.
See also Ex 34:19, 20; Lev 27:26.
Later a change was implemented - God dedicated the Levites as priests for the nation in place of all the first born sons of Israel.
Num 3:12, 13 - Now, behold, I have taken the Levites from among the
sons of Israel instead of every firstborn, the first issue of the womb
among the sons of Israel. So the Levites shall be Mine. “For all the
firstborn are Mine; on the day that I struck down all the firstborn in
the land of Egypt, I sanctified to Myself all the firstborn in Israel,
from man to beast. They shall be Mine; I am the LORD.”
However, the firstborn must be redeemed with money under this arrangement:
Ex 34:19, 20 - “The first offspring from every womb belongs to Me, and
all your male livestock, the first offspring from cattle and sheep.
“You shall redeem with a lamb the first offspring from a donkey; and
if you do not redeem it, then you shall break its neck. You shall
redeem all the firstborn of your sons. None shall appear before Me
This was lasting ordinance in Israel.