For the law of Moses appoints [morally] weak men to be head priests, but the message of [God's] oath, which came after that law [Note: The quotation from Psa. 110:4 (See verse 21) was written after the law of Moses was given] appointed the Son, who was made perfect [in every way] forever.

Therefore, when Christ came into the world, He said [to God], [Psa. 40:6-8 LXX], "You did not want an [animal] sacrifice and an offering, but you prepared a body for me [to sacrifice].

because God had planned to give us something better [than they got], so that they would not be complete without us. [Note: The idea here is that these faithful people of Old Testament times did not receive the fullest of blessings until Christ came to make them available to both them and us together].