וַיַּ֜עַן וַיֹּ֤אמֶר אֵלַי֙ לֵאמֹ֔ר זֶ֚ה דְּבַר־יְהוָ֔ה אֶל־זְרֻבָּבֶ֖ל לֵאמֹ֑ר לֹ֤א בְחַ֙יִל֙ וְלֹ֣א בְכֹ֔חַ כִּ֣י אִם־בְּרוּחִ֔י אָמַ֖ר יְהוָ֥ה צְבָאֽוֹת׃
Then he answered and spoke unto me, saying: ‘This is the word of the LORD unto Zerubbabel, saying: Not by might, nor by power, but by My spirit, saith the LORD of hosts.
Read midrashic interpretation of Zechariah 4:6: and classical rabbinic exegesis.