Who are the natural branches in Romans 11?

The natural branches are the nation of Israel. In Romans 11, Paul pictures Israel as the natural branches of a good olive tree, broken off and set aside, while Gentiles are wild branches grafted in contrary to nature. God will graft Israel, the natural branches, back into their own olive tree.

Les explains that Romans 11 contrasts Israel, the natural branches of the good olive tree, with Gentiles, who are like a wild, unproductive olive tree. God broke off natural Israel and set them aside for a time, grafting in Gentiles by grace to share the fatness of the Abrahamic promises. But He is not through with Israel; He will graft the nation back into their own olive tree. Gentiles must be careful, for if they reject, they too can be cut off.

Romans 11:24

For if thou wert cut out of the olive tree which is wild by nature, and wert graffed contrary to nature into a good olive tree: how much more shall these, which be the natural branches, be graffed into their own olive tree?

What did God do with Israel and the Gentiles in Romans 11?

God temporarily broke off natural Israel and grafted Gentiles, pictured as a wild olive tree, into the fatness of the Abrahamic promises by grace. Yet if Gentiles reject Him, they too will be cut off, and God will graft Israel back into their own olive tree and turn again to His covenant people.