What does Zechariah 4:6 mean?

He said, 'This is what the LORD says to Zerubbabel: It's not by force or by power, but by my Spirit, says the LORD who rules over everything.' Zechariah 4:6 - Modern Text Bible

(God tells Zerubbabel that success won't come from human strength, but only through God's Spirit. It's a message of dependence on God.)