What does “Not by might, nor by power, but by my Spirit” warn against? (Zech. 4:6)

This is the word of the Lord to Zerub′babel: Not by might, nor by power, but by my Spirit, says the Lord of hosts. (Zech. 4:6) The word חַיִל is usually translated as "might" here. But more often it means "army," by a…