Treasury of Scripture Knowledge

Summary

Because all the firstborn are mine; for on the day that I smote all the firstborn in the land of Egypt I hallowed unto me all the firstborn in Israel, both man and beast: mine shall they be: I am the LORD.

Bible References

Because

Numbers 8:16
For they have been given to me from among the children of Israel; in place of every mother's first son, the first to come to birth in Israel, I have taken them for myself.
Numbers 18:15
The first birth of every living thing which is offered to the Lord, of man or beast, is to be yours; but for the first sons of man payment is to be made, and for the first young of unclean beasts.
Exodus 13:2
Let the first male child of every mother among the children of Israel be kept holy for me, even the first male birth among man or beast; for it is mine.
Exodus 22:29
Do not keep back your offerings from the wealth of your grain and your vines. The first of your sons you are to give to me.
Exodus 34:19
Every first male child is mine; the first male birth of your cattle, the first male of every ox and sheep.
Leviticus 27:26
But a man may not give by oath to the Lord the first-fruits of cattle which are offered to the Lord: if it is an ox or a sheep it is the Lord's.
Ezekiel 44:30
And the best of all the first-fruits of everything, and every offering which is lifted up of all your offerings, will be for the priests: and you are to give the priest the first of your bread-making, so causing a blessing to come on your house.
Luke 2:23
(As it says in the law of the Lord, Every mother's first male child is to be holy to the Lord),
Hebrews 12:23
To the great meeting and church of the first of those who are named in heaven, and to God the judge of all, and to the spirits of good men made complete,

On the day

Exodus 12:29
And in the middle of the night the Lord sent death on every first male child in the land of Egypt, from the child of Pharaoh on his seat of power to the child of the prisoner in the prison; and the first births of all the cattle.
Exodus 13:15
And when Pharaoh made his heart hard and would not let us go, the Lord sent death on all the first sons in Egypt, of man and of beast: and so every first male who comes to birth is offered to the Lord; but for all the first of my sons I give a price.

Basic English, produced by Mr C. K. Ogden of the Orthological Institute - public domain