Zechariah sees a lampstand that is continually kept burning by an unlimited reservoir of oil. This picture reminds the people that it is only through God's Spirit that they will succeed, not by their own might and resources.
Not by might
nor by power,
but by my Spirit!!
As you live for God,
don't trust in your own strength!
Instead, trust in God & the work of the Holy Spirit
to work out every detail of your lives.