For every high priest is appointed to offer gifts and sacrifices; therefore it was necessary for this [priest] also to have something to offer.
Now if He were on earth, He wouldn't be a priest, since there are those offering the gifts prescribed by the law.
References for Hebrews 8:4
These serve as a copy and shadow of the heavenly things, as Moses was warned when he was about to complete the tabernacle. For He said, Be careful that you make everything according to the pattern that was shown to you on the mountain.
References for Hebrews 8:5