'First born' in the Bible

The sons of Reuben, Israel’s (Jacob’s) firstborn, their generations, by their families (clans), by their fathers’ households, according to the number of names, head by head, every male from twenty years old and upward, all who were able to go to war:

These are the names of the sons of Aaron: Nadab the firstborn, Abihu, Eleazar, and Ithamar.

“Behold, I have taken the Levites from among the sons of Israel instead of and as a substitute for every firstborn, that is, the first that opens the womb among the Israelites. So the Levites shall be Mine,

for all the firstborn are Mine. On the day that I killed all the firstborn in the land of Egypt, I consecrated for Myself all the firstborn in Israel, both man and animal. They shall be mine; I am the Lord.”

Then the Lord said to Moses, “Number every firstborn male of the Israelites from a month old and upward, and make a list of their names.

You shall take the Levites for Me instead of and as a substitute for all the firstborn among the Israelites. I am the Lord; and you shall take the cattle of the Levites instead of and as a substitute for all the firstborn among the cattle of the Israelites.”

So Moses numbered all the firstborn among the Israelites, just as the Lord had commanded him;

and all the firstborn males from a month old and upward as numbered were 22,273 [273 more than the Levites].

“Take the Levites [for Me] instead of all the firstborn among the sons of Israel, and the cattle of the Levites instead of their cattle. And the Levites shall be Mine. I am the Lord.

For the ransom (redemption price) of the 273 of the firstborn of the Israelites who outnumber the Levites,

from the firstborn of the Israelites he took the money in terms of the sanctuary shekel, 1,365 shekels.

for they are wholly given to Me from among the Israelites. I have taken them for Myself instead of all who are born first, the firstborn of all the Israelites.

For all the firstborn among the Israelites are Mine, among the men and among the animals; on the day that I struck down every firstborn in the land of Egypt, I sanctified and set the Israelites apart for Myself.

And I have taken the Levites instead of every firstborn among the Israelites.

Every firstborn of the womb of all flesh, whether it is man or animal, which they bring to the Lord, shall be yours; nevertheless, the firstborn of man you shall most certainly redeem, and the firstborn of unclean animals you shall redeem.

But the firstborn of a cow or of a sheep or of a goat you shall not redeem; they are holy [and belong to the Lord]. You shall sprinkle their blood on the altar and shall offer up their fat in smoke as an offering by fire, for a sweet and soothing aroma to the Lord.

Reuben, the firstborn of Israel (Jacob), the sons of Reuben: of Hanoch, the family of the Hanochites; of Pallu, the family of the Palluites;

while the Egyptians were burying all their firstborn whom the Lord had struck down among them. Upon their gods the Lord also executed judgments.