Numbers 3:13

13 For every first-born mine; in the day in which I smote every first-born in the land of Egypt, I sanctified to myself every first-born in Israel: both of man and beast, they shall be mine: I the Lord.

Numbers 3:13 Meaning and Commentary

Numbers 3:13

Because all the firstborn [are] mine
Not merely in a general way, as all creatures are his, but in a special manner as his own, and that for the following reason:

[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;
that is, sanctified or set them apart as his own special property, or ordered the people of Israel so to do, ( Exodus 13:2 ) ; for as when he destroyed the firstborn of the Egyptians, he saved the firstborn of Israel, he had a special claim upon them as his; and though it was in the night when he destroyed the firstborn of Egypt, yet it was the night which preceded that day, and was a part of that day, even the fifteenth of Nisan, when the instructions were given to sanctify all the firstborn; though, as Aben Ezra observes, "day" signifies "time", so that it was at or about the same time that the one and the other were done:

mine they shall be;
this was declared when they were ordered to be sanctified to him, but now they were to be exchanged for the Levites:

I [am] the Lord;
who have sovereign power to do as he would in claiming the firstborn, and then in exchanging them for the Levites, and appointing the Levites to minister to the priests, and serve in the tabernacle.

Numbers 3:13 In-Context

11 And the Lord spoke to Moses, saying,
12 Behold, I have taken the Levites from the midst of the children of Israel, instead of every male that opens the womb from among the children of Israel: they shall be their ransom, and the Levites shall be mine.
13 For every first-born mine; in the day in which I smote every first-born in the land of Egypt, I sanctified to myself every first-born in Israel: both of man and beast, they shall be mine: I the Lord.
14 And the Lord spoke to Moses in the wilderness of Sina, saying,
15 Take the number of the sons of Levi, according to the houses of their families, according to their divisions; number ye them every male from a month old and upwards.

The Brenton translation of the Septuagint is in the public domain.