It is written:
“Yes, He shall build the temple of the LORD. He shall bear the glory, And shall sit and rule on His throne; So He shall be a priest on His throne, And the counsel of peace shall be between them both.”” (Zechariah 6:13)
We are told in this passage that the Messiah would be a High Priest when He ruled on HIs throne. This means that whenever Christ assumed His work as a High Priest, He would also be reigning as a King on His throne.
So if Christ is High Priest right now, then He is reigning now on HIs throne.
With that in mind, consider the following passages:
Hebrews 3:1-Therefore, holy brethren, partakers of the heavenly calling, consider the Apostle and High Priest of our confession, Christ Jesus,
Hebrews 4:14-16-Seeing then that we have a great High Priest who has passed through the heavens, Jesus the Son of God, let us hold fast our confession. 15 For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin. 16 Let us therefore come boldly to the throne of grace, that we may obtain mercy and find grace to help in time of need.
Hebrews 6:20-where the forerunner has entered for us, even Jesus, having become High Priest forever according to the order of Melchizedek.
Hebrews 7:24-But He, because He continues forever, has an unchangeable priesthood.
Perhaps the writer of Hebrews had this prophecy of Zechariah in mind, since he also points out that Christ is reigning as High Priest, even now:
Hebrews 1:3-who being the brightness of His glory and the express image of His person, and upholding all things by the word of His power, when He had by Himself purged our sins, sat down at the right hand of the Majesty on high,
Hebrews 10:12-13-But this Man, after He had offered one sacrifice for sins forever, sat down at the right hand of God, 13 from that time waiting till His enemies are made His footstool.
Hebrews 12:1-2-Therefore we also, since we are surrounded by so great a cloud of witnesses, let us lay aside every weight, and the sin which so easily ensnares us, and let us run with endurance the race that is set before us, 2 looking unto Jesus, the author and finisher of our faith, who for the joy that was set before Him endured the cross, despising the shame, and has sat down at the right hand of the throne of God.
Today Jesus reigns from Mount Zion, the city of the living God, heavenly Jerusalem, with an innumerable company of angels (Hebrews 12:22).