Jerome
Patristic
c. A.D. 347–420
“Every only child is a firstborn child; but not every firstborn is an only child. A firstborn child is not only one after whom other children are also born but also one before whom no other child is born. "All that opens the womb," says the Lord to Aaron, "of all flesh that are offered to the Lord, of men and beasts, shall belong to you; only the firstborn of men shall be redeemed with a price and the firstborn of beasts that are unclean." The Word of God defined what was meant by a "firstborn." "All," it says, "that opens the womb." Otherwise, if no child is a firstborn child but only one who subsequently has brothers, the firstborn are not due the priests until others are also born, lest perchance a child be an only child and not the firstborn child, in the event that no other child shall be born subsequently.”