Albert Barnes Commentary Zechariah 4:6

"Then he answered and spake unto me, saying, This is the word of Jehovah unto Zerubbabel, saying, Not by might, nor by power, but by my Spirit, saith Jehovah of hosts." — Zechariah 4:6 (ASV)

This is the word of the Lord to Zerubbabel - Osorius: “It is as if he were to say, the meaning of the vision and scope of what has been shown is, ‘God’s actions have almost cried aloud to Zerubbabel that all these visions will come to an end in their time, not accomplished by human might nor by fleshly strength, but by the power of the Holy Spirit and through Divine Will.’

“For the Only Begotten became Man as we are, but He did not wage war according to the flesh to set up the Church as a candlestick to the world. Nor did He, through physical weapons and armed phalanxes, make those two peoples His own or place the spiritual lights on the candlestick. Instead, by the might of His own Spirit, He appointed in the Church first Apostles, then prophets and evangelists (1 Corinthians 12:28), and all the rest of the holy company, filling them with divine gifts and enriching them abundantly by the outpouring of His Spirit.”

Cyril: “The work of Christ, then, was not accomplished by great power or by fleshly might, but by the power of the Spirit Satan was despoiled, and the ranks of the opposing powers fell with him; and Israel and those who formerly served the creature rather than the Creator were called to the knowledge of God through faith. But that He saved all under heaven, not by human arm, but by His own power as God Emmanuel, Hosea also testified, I will have mercy upon the house of Judah and will save them by the Lord their God, and will not save them by bow nor by sword nor by battle nor by chariots nor by horses nor by horsemen (Hosea 1:7). But exceedingly fittingly was this said to Zerubbabel, who was of the tribe of Judah and at that time administered the royal seat at Jerusalem.”

So that he might not think that, since such glorious successes were foretold to him, wars would, in due time, have to be organized, God lifts him up from these unsound and human thoughts and instructs him to be of this mind: that the force was divine—the might of Christ, who would bring such things to pass—and not human.

Having given this key to the whole vision, without explaining its details, God expands on what He had said to Zerubbabel, as He had in the preceding chapter to Joshua (Zechariah 3:8–10).