The reality of this verse is that God is promising the exiles who are returning to Jerusalem that a great Deliverer is coming. This is a Messianic promise. It calls the Messiah “the Branch”, hearkening back to Jeremiah’s pre-exilic words of prophecy. And the Deliverer comes as a servant to the nation.
The scene in which this promise is made reads like the kind of thing recorded in the epic poetry of Job. Joshua (or Yeshua – Greek: Jesus) is the high priest who has returned to Jerusalem to re-institute temple worship. (Zechariah 3:1-3) We also read about him in Ezra and Nehemiah. In this vision, Zechariah sees the priest standing before the angel of the Lord, with Satan standing to the right of him, accusing him before the Lord. And God rebukes the devil. It seems that Satan is wanting to accuse Joshua of being unfit to be a priest. He is clothed in filthy garments. And God just takes care of that. (Zechariah 3:4-5)
The rest of chapter three is an address to the high priest in which God assures him and comforts him.(Zechariah 3:6-7) He promises that if Joshua will walk in His ways, God will bless the work of his priesthood. And then God re-affirms the promise to bring His servant, the Branch to the nation. The faithful nation, restored to its land, worshipping the Lord, would eventually see the Messiah come. This is still hundreds of years away, but to Joshua the high priest is given the promise of Jesus, the Great High Priest. And after that promise, God paints a beautiful picture of peace under the rule of Branch (Zechariah 3:9-10)
To the first post-exilic high priest that also bore Jesus’ own name, God gave the promise of the Messiah. He affirmed this priest with a promise. He removed the iniquity of that priest to show that God could use someone for His purposes. He assured the nation of His unfailing love and power to forgive. And He promised a future… one that I know today, yet still anticipate in its completion.