The Olive Tree described in the lyrics of this song are described in the Bible verses (see below)
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Romans 11:17 And if some of the branches were broken off, and you, being a wild olive tree, were grafted in among them, and with them became a partaker of the root and fatness of the olive tree,
Romans 11:24 For if you were cut out of the olive tree which is wild by nature, and were grafted contrary to nature into a cultivated olive tree, how much more will these, who are natural branches, be grafted into their own olive tree?
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