Hebrews 8:4
For if he were on earth, he should not be a priest, seeing that there are priests that offer gifts according to the law: For if he were on earth, he should not be a priest, seeing that there are priests that offer gifts according to the law:
If He were on earth He would not serve as priest, for priests appointed under the law already fill that place by offering gifts, while His own priestly ministry is exercised in the heavenly sanctuary and not in the earthly one. His priesthood is not an earthly priesthood under the law where other priests offer gifts. The earthly sanctuary and tabernacle were made as a pattern of the heavenly sanctuary, bearing witness to heavenly things and to Him.
The Jewish priesthood and its sacrifices were a shadow of His ministry. His death fulfilled the sacrificial offerings as the atonement for sin once for all, and His work as High Priest in heaven revealed their meaning. He is the true High Priest who comes into office when type and shadow meet their reality, at the time when Caiaphas was in office.
The heavenly sanctuary and its ministry, together with its earthly pattern, are to be kept clear and distinct in the minds of God's people.