John Calvin Commentary Hebrews 8:4

"Now if he were on earth, he would not be a priest at all, seeing there are those who offer the gifts according to the law;" — Hebrews 8:4 (ASV)

For if he were on earth, etc. It is now beyond dispute that Christ is a high priest. But, just as the office of a judge does not exist without laws and statutes, so the office of sacrificing must be connected with Christ as a priest. Yet he has no earthly or visible sacrifice; therefore, he cannot be a priest on earth.

We must always hold this truth: when the Apostle speaks of the death of Christ, he does not regard the external action, but the spiritual benefit. He suffered death as humans do, but as a priest, he atoned for the sins of the world in a divine manner. There was an external shedding of blood, but there was also an internal and spiritual purgation. In a word, he died on earth, but the power and efficacy of his death proceeded from heaven.

What immediately follows, some render this way: “He could not be a priest of the number of those who offer gifts according to the Law.” But the words of the Apostle mean another thing, and therefore I prefer this rendering: “He could not be a priest as long as there are priests who,” etc. For he intends to show one of these two things: either that Christ is no priest while the priesthood of the Law continued (as he had no sacrifice), or that the sacrifices of the Law ceased as soon as Christ appeared. The first of these is against all reason, for it is an act of impiety to deprive Christ of his priesthood. It then remains for us to confess that the Levitical order is now abolished.