John Chrysostom

"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. …

Homily on Romans 19 ↗

Theophylact of Ohrid

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 is, into the patriarchs, then how much more will the Jew, to whom good is akin by nature, be returned to his own olive tree, that is, to his own fathers? And when you hear Paul say "by nature," understand it as: naturally and logically — for example: it was natural that the son of holy Abraham would be holy. …

Commentary on Romans ↗

Thomas Aquinas

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 generation, and their malice natural (Wis 12:10); we were by nature children of wrath (Eph 2:3); and were grafted into the good olive tree, i.e., into the faith of the Jews, contrary to nature, i.e., against the common course of nature. …

Commentary on Romans ↗