Olive trees were native to the Mediterranean area where Paul and the Romans lived. Not only did they grow fruit that was used to make all kinds of important oils, olive branches also traditionally represented peace and harmony.
In Romans, Paul has God hack an olive tree to bits. Not exactly the peace and tranquility we were expecting.
Paul is trying to warn the Gentile-Christians not to get so high and mighty about their new place in God's family. They may think they've got one over on the non-believing Jews, but the truth is, God still digs them. Paul writes:
If the root is holy, then the branches also are holy. But if some of the branches were broken off, and you, a wild olive shoot, were grafted in their place to share the rich root of the olive tree, do not boast over the branches. If you do boast, remember that it is not you that support the root, but the root that supports you. (11:16-18)
So the Gentile-Christians need to remember not to brag about their good fortune. They've also got to realize that the Jewish faith is like the roots of their tree. Without it, they would be nothing. Time to start showing some respect, guys.
Paul also continues with a tiny threat (just a tiny one):
Do not become proud, but stand in awe. For if God did not spare the natural branches, perhaps he will not spare you […] And even those of Israel, if they do not persist in unbelief, will be grafted in, for God has the power to graft them in again. For if you have been cut from what is by nature a wild olive tree and grafted, contrary to nature, into a cultivated olive tree, how much more will these natural branches be grafted back into their own olive tree. (11:20-24)
Yowza. Another strong message. Sure, the Jews have been cut off God's family tree, but God can also bring them back any time he wants to. God's a pretty good gardener, in case you're wondering.
As it turns out, the Gentiles don't even belong on this tree. According to Paul, it's native to Israel, and it's not natural that they—the "wild" branches—should be growing on it. God has been generous enough to graft them on where they didn't belong, but they better watch out. If they step out of line, they'll end up like the non-believers. Lying in a heap of twigs on the ground.
The Bible is filled with references to God, the Great Pruner:
• "The Lord cut off from Israel head and tail, palm branch and reed in one day." (Isaiah 9:14)
• "Go up through her vine-rows and destroy, but do not make a full end; strip away her branches, for they are not the Lord's." (Jeremiah 5:10)
• John's Gospel has a reference to God bringing out the pruning shears. "I am the vine, you are the branches […] Whoever does not abide in me is thrown away like a branch and withers; such branches are gathered, thrown into the fire, and burned." (John 15:5-6)
• Mormon author, Hugh B. Brown, tells the story of "The Currant Bush" with similar pruning themes.