Thus the Lord Jesus Christ was the firstborn and the only Son. St. Jerome was right when he said: “Every only son is a firstborn but not every firstborn is an only son.” The expression ‘firstborn’ does not mean that another is born after him but it means that no sibling was born before him. That is why the firstborn of the unclean animals could be redeemed when they were one month old (Num. 18: 16,17), and the first offspring of the clean animals were to be offered as sacrifices to God without waiting until the birth of another offspring. He is the firstborn, whether or not one is born after him, because he is the first offspring of the womb.