Zechariah 6:9 - Albert Barnes' Notes on the Bible

And the word of the Lord came to me - The visions being closed, Zechariah marks the change by adopting the usual formula, with which the prophets authenticated, that they spake not of themselves, but by the Spirit of God. The act enjoined is a symbolic act, pointing and summing up and interpreting the visions, as some of the visions had been already expanded by fresh revelations following immediately upon them.