Is not this direction concerning the firstborn, in allusion to the only begotten SON of GOD? Did not GOD our FATHER give and exchange, as it were, his firstborn and only SON, for the people of his everlasting love, when he gave him up to the service of the whole law, as their law-surety and sponsor; and to the death of the cross, in their law-room and stead? John 3:16.
Numbers 3:40-43
40 And the LORD said unto Moses, Number all the firstborn of the males of the children of Israel from a month old and upward, and take the number of their names.
41 And thou shalt take the Levites for me (I am the LORD) instead of all the firstborn among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel.
42 And Moses numbered, as the LORD commanded him, all the firstborn among the children of Israel.
43 And all the firstborn males by the number of names, from a month old and upward, of those that were numbered of them, were twenty and two thousand two hundred and threescore and thirteen.