NOTES for Zec 6:12
In the days when Zechariah preached—shortly after the Jews' return from the Babylonian exile, while members of the first generation of returning exiles were still alive—messianic expectations among the Jewish people were extraordinarily intense. This is hardly surprising: both the pre-exilic prophets and Isaiah of Babylon, who began preaching shortly before the Persian conquest of Babylonia and Cyrus the Great's decree allowing the Jews to return to the land of their fathers, spoke of the end of the exile as a time of redemption, when all the people's past sins would be forgiven and all that remained would be to await the Messiah promised by God.
Yet the prophet's contemporaries held views of the Messiah that more closely resembled those of the early prophets: for them the Deliverer was above all a righteous ruler who, on coming to power, would establish laws in the country consistent with the Torah and restore the Temple in Jerusalem, resuming regular worship there, including, naturally, sacrifices. Zechariah tries to explain to them that the Messiah is not at all as they expect Him to be. The prophet sees Him first and foremost as a high priest, and only then as a ruler. In a sense, he brings his listeners back to the image of David—a prophet who, even after becoming king, remained a prophet above all. Apparently, however, this is not a high priest in the traditional sense of the word. It is no accident that Zechariah calls the Messiah a shoot or branch that grows 'from its own root' or 'in its own soil'; the corresponding Hebrew word literally means 'from its own depths'. In this way the prophet evidently means to say that, as regards His ministry, the Messiah does not depend on the laws of the untransformed world, that He is not conditioned by them and needs neither an official position nor social status to fulfil His mission.
Zechariah speaks of the Messiah's 'own root' in much the same sense in which his great predecessor, Isaiah of Babylon, calls the Messiah a 'servant' or a 'youth': He does not need to be a great man in the eyes of 'this world' to accomplish what God sends Him into the world to do. For the Messiah's Kingdom, in His own words, is 'not of this world'. Neither He Himself nor His Kingdom needs the support of this world's powers.