[17] And if some of the branches be broken off, and thou, being a wild olive tree, wert graffed in among them, and with them partakest of the root and fatness of the olive tree;
Clearly! God is using a wild olive tree to symbolize the Gentile nations, and the natural Olive Tree to symbolize the representation of Covenant Israel into which believers are grafted in. For example, we, join with Paul, and the Apostles into Chirst, the TRUE ISRAEL of God, Ephesians 2:11-19), which this covenant tree merely represents. This is the New Covenant Church, and its is symbolized by the olive tree having Gentiles grafted into it that they become heirs (right along with the believing Jews) according to the promised made to Israel.
Likewise in Zechariah chapter four, the symbolism of two olive trees and the candlestick (lampstand) are signifying the Church.
Zechariah 4:2-6 KJV
[2] And said unto me, What seest thou? And I said, I have looked, and behold a candlestick all of gold, with a bowl upon the top of it, and his seven lamps thereon, and seven pipes to the seven lamps, which are upon the top thereof:
[3] And two olive trees by it, one upon the right side of the bowl, and the other upon the left side thereof.
[4] So I answered and spake to the angel that talked with me, saying, What are these, my lord?
[5] Then the angel that talked with me answered and said unto me, Knowest thou not what these be? And I said, No, my lord.
[6] Then he answered and spake 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.
The Lampstands and olive trees stand before God, not by their own power or by their own might, but by the Holy Spirit of the Lord. This again illustrating what we've been seeing of the two Witnesses. It is not by any power we have inherently, but because of the power of the Holy Spirit of God given us that we witness or have the testimony of Christ. Not by our own oil, but by the pure oil of the Olive tree. Not by our own light, but by the light of the candle. The two olive trees symbolize the anointed ones that stand by the Lord of the whole earth (Zechariah 4:14), not by their own power, but by power of God. This symbolizes the Church, anointed by the Spirit of God. Just as we read that the two Witnesses of Revelation also stand by the Lord of the earth.