For if thou - If you who are Gentiles.
Wert cut out of - Or, if thou wert of the cutting of the wild olive-tree.
Which is wild by nature - Which is uncultivated and unfruitful. That is, if you were introduced into a state of favor with God from a condition which was one of enmity and hostility to him. The argument here is, that it was in itself as difficult a thing to reclaim them, and change them from opposition to God to friendship, as it would seem difficult or impossible to reclaim and make fruitful the wild olive-tree.
And were graffed contrary to nature - Contrary to your natural habits, thoughts, and practices. There was among the Gentiles no inclination or tendency toward God. This does not mean that they were physically depraved, or that their disposition was literally like the wild olive; but it is used, for the sake of illustration, to show that their moral character and habits were unlike those of the friends of God.
How much more ... - The meaning of this whole verse may be thus expressed; “If God had mercy on the Gentiles, who were outcasts from his favor, shall he not much rather on those who were so long his people, to whom had been given the promises, and the covenants, and the Law, whose ancestors had been so many of them his friends, and among whom the Messiah was born?” In some respects, there are facilities among the Jews for their conversion, which had not existed among the Gentiles. They worship one God; they admit the authority of revelation; they have the Scriptures of the Old Testament; they expect a Messiah; and they have a habit of professed reverence for the will of God.