Luke 2:23

As it is written in the law of the Lord,.... In Exodus 13:2

every male that openeth the womb, shall be called holy to the Lord; that is, devoted and consecrated to him, and so to be redeemed. The reason of this law was this, when God smote all the firstborn of Egypt, he saved the firstborn of Israel; and therefore claimed a right to them, and obliged their parents, excepting the Levites, to redeem them at the price of five shekels, which were about twelve shillings and six pence of our money, and which was given to the Levites: see Exodus 13:12 And this law our Lord came under as Mary s firstborn, and as one holy to the Lord; and such a sum of money was now paid for his redemption, who was the great Redeemer of his people: he being made under the law, and in all things subject to it, that he might redeem them from the bondage, curse, and condemnation of it. Now as the tribe of Levi was excepted from this law, it is a clear case, that Mary, though allied to Elisabeth, was not of the tribe of Levi, otherwise her firstborn would not have been subject to it y.

"An Israelite that comes from a priestess, or from a she Levite, is free, (i.e. from the redemption of the firstborn;) for the thing does not depend on the father, but on the mother, as it is said, that openeth the womb in Israel.''

y Maimon. Hilch. Biccurim c. 11. sect. 10.