How was Melchizedek a picture of Christ as high priest?
Melchizedek served as high priest of all, prefiguring Christ as high priest. Christ entered a greater, more perfect tabernacle not made with hands—heaven itself—not by the blood of goats and calves, but by His own blood, once for all time, obtaining eternal redemption.
Les explains that just as Aaron was the high priest of Israel, Melchizedek was the high priest of all, serving as a picture of Christ our high priest. But Christ's priesthood is greater: He went by a greater and more perfect tabernacle, not made with hands, not of this creation, but in heaven. There He entered the Holy of Holies once, not just once a year, but once for all time, neither by the blood of goats and calves, but by His own blood, having obtained eternal redemption for us. What did He present in the Holy of Holies in heaven? His own blood.