Albert Barnes Commentary Zechariah 4:2

"And he said unto me, What seest thou? And I said, I have seen, and, behold, a candlestick all of gold, with its bowl upon the top of it, and its seven lamps thereon; there are seven pipes to each of the lamps, which are upon the top thereof;" — Zechariah 4:2 (ASV)

And I said, I have looked and behold a candlestick all of gold - The candlestick is the seven-branched candlestick of the tabernacle (Exodus 25:31), but with variations purposely introduced to symbolize the fuller and more constant supply of the oil, itself the symbol of God’s Holy Spirit, who:

“Enables with perpetual light
The dullness of our blinded sight.”

The first variation is “her bowl on the top of the candlestick,” which contains the oil. Then, dependent on this, are the pipes that derive the oil into each lamp: “seven several pipes to the seven lamps,” that is, seven pipes for each lamp. And there are the two olive trees on either side of the bowl, whose extreme and fine branches poured the golden oil through two golden pipes into the bowl that supplied the lamps.

The multiplied conduits imply the large and perfect supply of oil, unceasingly supplied. The number seven is symbolic of perfection or of the reconciling of God (symbolized by three) to the world (symbolized by four, its four quarters). The spontaneous flow of the golden oil from the olive trees symbolizes the free gift of God.