Jamieson, Fausset and Brown on Romans 11:15

15. For if the casting away of them--The apostle had denied that they were east away (Ro 11:1); here he affirms it. But both are true; they were cast away, though neither totally nor finally, and it is of this partial and temporary rejection that the apostle here speaks.

be the reconciling of the--Gentile

world, what shall the receiving of them be, but life from the dead?--The reception of the whole family of Israel, scattered as they are among all nations under heaven, and the most inveterate enemies of the Lord Jesus, will be such a stupendous manifestation of the power of God upon the spirits of men, and of His glorious presence with the heralds of the Cross, as will not only kindle devout astonishment far and wide, but so change the dominant mode of thinking and feeling on all spiritual things as to seem like a resurrection from the dead.