Romans 11:24

"But if the firstfruits are holy, so is the lump; and if the root is holy, so are the branches. But if some of the branches were broken off, and you, though you were a wild olive, were grafted in among them and became a sharer in the root and the fatness of the olive tree, do not boast against the branches. But if you do boast, it is not you who bear the root, but the root you. You say then: The branches were broken off so that I might be grafted in. Well: they were broken off because of unbelief. But you stand by faith: do not be proud in your thinking, but fear. For if God did not spare the natural branches, neither will he spare you. Behold, then, the goodness and the severity of God: toward those indeed who fell, severity; but toward you, goodness, if you continue in goodness. Otherwise you too will be cut off, and they, if they do not continue in unbelief, will be grafted in. For God is able to graft them in again. For if you were cut out of the olive tree which is wild by nature, and contrary to nature were grafted into the good olive tree, how much more shall these, who are according to nature, be grafted into their own olive tree?" I do not know how those who come from the school of Valentinus and Basilides, failing to hear these things thus spoken by Paul, suppose that there is a nature of souls which is always saved and never perishes, and another which always perishes and is never saved: when Paul plainly says that the branches of the good olive tree were broken off because of their own unbelief, and stood in need of the vengeance of divine severity; and again that the branches of the wild olive — which among them is set down as a nature that is lost — were grafted into the root and fatness of the olive tree. But to those people, indeed, an easy answer may be given by these words. […]

"For God is able," he says, "to graft them in again," since He doeth things beyond expectation. But if thou wishest for things to be in order, and reasons to be consecutive, you have from yourselves a demonstration which more than meets your wants. "For if thou wert cut out of the olive tree, which is wild by nature, and were grafted contrary to nature into a good olive tree, how much more shall these, which be the natural branches, be grafted into their own olive tree." If then faith was able to do what was contrary to nature, much more will it that which is according to nature. For if this person, who was cut off from those by nature his fathers, came contrary to nature unto Abraham, much more wilt thou be able to recover thine own. For the Gentile's evil lot is according to nature (he being by nature a wild olive), and the good contrary to nature (it being contrary to nature for him to be grafted into Abraham), but thy lot on the contrary is the good by nature. For it is not upon another root, as the Gentile, but on thine own that thou art to be fixed if thou art minded to come back. What then dost thou deserve, when after the Gentile had been able to do what was contrary to nature, thou art not able to do that which is according to nature, but hast given up even this? Then as he had said "contrary to nature," and, "wert grafted in," that you may not suppose the Jew to have the advantage, he again corrects this by saying that he also is grafted in. […]

The olive tree represents faith, whereas the wild olive refers to wickedness.

Second, by arguing from the lesser, saying: for if you, O gentile, were cut out of the wild olive tree, i.e., from gentileness, which by nature was not fruit-bearing, not as God made nature, but because it was spoiled by sin: they were a wicked …

If, he reasons, if you, a Gentile, to whom evil is akin by nature and who has ancestors resembling a wild olive tree, were cut off from them by faith, and, what was not in your nature, were grafted into the good olive tree, that …