For I would not, brethren, that ye should be ignorant of this mystery, lest ye should be wise in your own conceits; that blindness in part is happened to Israel, until the fulness of the Gentiles be come in. I would not - that ye should be ignorant of this mystery - Mystery, μυστηριον, signifies any thing that is hidden or covered, or not fully made manifest. The Greek word seems to have been borrowed from the Hebrew מסתר mistar, from the root סתר sathar, to hide, conceal, etc.; though some derive it from μυεισθαι, to be initiated into sacred rites, from μυειν, to shut up. In the New Testament it signifies, generally, any thing or doctrine that has not, in former times, been fully known to men: or, something that has not been heard of, or which is so deep, profound, and difficult of comprehension, that it cannot be apprehended without special direction and instruction: here it signifies the doctrine of the future restoration of the Jews, not fully known in itself, and not at all known as to the time in which it will take place. In Romans 16:25 it means the Christian religion, not known till the advent of Christ. The apostle wished the Romans not to be ignorant of this mystery, viz. that such a thing was intended; and, in order to give them as much instruction as possible on this subject, he gives them some characteristic or sign of the times when it was to take place.
Lest ye should be wise in your own conceits - It seems from this, and from other expressions in this epistle, that the converted Gentiles had not behaved toward the Jews with that decorum and propriety which the relation they bore to them required. In this chapter the apostle strongly guards them against giving way to such a disposition.
Blindness in part is happened to Israel - Partial blindness, or blindness to a part of them; for they were not all unbelievers: several thousands of them had been converted to the Christian faith; though the body of the nation, and especially its rulers, civil and spiritual, continued opposed to Christ and his doctrine.
Until the fullness of the Gentiles be come in - And this blindness will continue till the Church of the Gentiles be fully completed - till the Gospel be preached through all the nations of the earth, and multitudes of heathens every where embrace the faith. The words πληρωμα των εθνων may be borrowed from the מלא הגוים melo haggoyim, a multitude of nations, which the Septuagint translate by πληθος εθνων. By the πληρωμα, or fullness, a great multitude may be intended, which should be so dilated on every hand as to fill various regions. In this sense the words were understood by Solomon ben Melec, ארצות הגוים שימלאו מהם. The nations of the Gentiles shall be filled with them: the apostle, therefore, seems to give this sense of the mystery - that the Jews will continue in a state of blindness till such time as a multitude of nations, or Gentiles, shall be converted to the Christian faith; and the Jews, hearing of this, shall be excited, by a spirit of emulation, to examine and acknowledge the validity of the proofs of Christianity, and embrace the faith of our Lord Jesus Christ.
We should not restrict the meaning of these words too much, by imagining,
1. That the fullness must necessarily mean all the nations of the universe, and all the individuals of those nations: probably, no more than a general spread of Christianity over many nations which are now under the influence of Pagan or Mohammedan superstition may be what is intended.
2. We must not suppose that the coming in here mentioned necessarily means, what most religious persons understand by conversion, a thorough change of the whole heart and the whole life: the acknowledgment of the Divine mission of our Lord, and a cordial embracing of the Christian religion, will sufficiently fulfill the apostle's words. If we wait for the conversion of the Jews till such a time as every Gentile and Mohammedan soul shall be, in this especial sense, converted to God, then - we shall wait for ever.