Exodus 13:15

15 Pharaoh was stubborn. He refused to let us go. So the LORD killed every oldest son in Egypt. He also killed every male animal that was born first to its mother. That's why I sacrifice to the LORD every male animal that was born first. And that's why I buy back each oldest son for him.'

Exodus 13:15 Meaning and Commentary

Exodus 13:15

And it came to pass, when Pharaoh would hardly let us go
Showed great reluctance to it, and with difficulty was prevailed upon to dismiss them: that the Lord slew all the firstborn in the land of Egypt, both the
firstborn of men, and the firstborn of beast:
which he did in one night, making use of a destroying angel or angels for that purpose: therefore I sacrifice to the Lord all that openeth thee matrix, being
males;
that is, the firstborn of all clean creatures, as oxen, sheep, and goats: but all the firstborn of my children I redeem;
by paying five shekels apiece to the priest for them, as before observed; and this law continues to be observed with the Jews; the manner of which, as related by Leo Modena F9, is as follows,

``Thirty days being expired after the birth of the child, they call a priest to them; that is to say, one that is descended of the stock of Aaron, whom the father of the child pleaseth; and so, many people being gathered together at the time appointed, the father of the child bringeth before the priest, in a bowl or basin, a good quantity of gold and silver, and then they give him the child into his arms; the priest then calling the mother of it before him, saith unto her, mistress, is this your son? she answereth, yes; then, replies he, have you never had any child before, either male or female, or have miscarried anyone? she saith unto him, no; then doth the priest say, this child is mine, as being the firstborn; then turning himself toward the father, he asketh him, whether he will redeem it or not? who answereth him, saying, see, here is gold and silver, take your own price; then saith the priest unto him, you will redeem it then? the father answereth, I will redeem it; it shall be so then, saith the priest, this child is mine as being the firstborn, as it is written, ( Numbers 18:16 ) . I therefore take this in exchange and so he takes the sum of two French crowns, or thereabout, as he thinks good, and then delivers the child to his father and mother, and this day they make a feasting day.''
This custom was used in Christ's time, and was observed with respect to him, ( Luke 2:27 ) .
FOOTNOTES:

F9 History of the Jews, par. 4. c. 9. sect. 2.

Exodus 13:15 In-Context

13 By sacrificing a lamb, buy back every male donkey that is born first to its mother. But if you don't buy the donkey back, break its neck. Buy back every oldest son.
14 "In days to come, your son will ask you, 'What does this mean?' "When he does, say to him, 'The LORD used his mighty hand to bring us out of Egypt. That's the land where we were slaves.
15 Pharaoh was stubborn. He refused to let us go. So the LORD killed every oldest son in Egypt. He also killed every male animal that was born first to its mother. That's why I sacrifice to the LORD every male animal that was born first. And that's why I buy back each oldest son for him.'
16 "This day will be like a mark on your hand. It will be like a sign on your forehead. It will remind you that the LORD used his mighty hand to bring us out of Egypt."
17 Pharaoh let the people go. The shortest road from Goshen to Canaan went through the Philistine country. But God didn't lead them that way. God said, "If they have to go into battle, they might change their minds. They might return to Egypt."
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