I say the truth - In what I am about to affirm respecting my attachment to the nation and people.
In Christ - Most interpreters regard this as a form of an oath, as equivalent to calling Christ to witness. It is certainly to be regarded, in its obvious sense, as an appeal to Christ as the searcher of the heart, and as the judge of falsehood. Thus, the word translated “in” ἐν en is used in the form of an oath in Matthew 5:34-36; Revelation 10:6, Greek. We are to remember that the apostle was addressing those who had been Jews; and the expression has all the force of an oath “by the Messiah.” This shows that it is right on great and solemn occasions, and in a solemn manner, and thus only, to appeal to Christ for the sincerity of our motives, and for the truth of what we say. And it shows further, that it is right to regard the Lord Jesus Christ as present with us, as searching the heart, as capable of detecting insincerity, hypocrisy, and perjury, and as therefore divine.
My conscience - Conscience is that act or judgment of the mind by which we decide on the lawfulness or unlawfulness of our actions, and by which we instantly approve or condemn them. It exists in every man, and is a strong witness to our integrity or to our guilt.
Bearing me witness - Testifying to the truth of what I say.
In the Holy Ghost - He does not say that he speaks the truth by or in the Holy Spirit, as he had said of Christ; but that the conscience pronounced its concurring testimony by the Holy Spirit; that is, conscience as enlightened and influenced by the Holy Spirit. It was not simply natural conscience, but it was conscience under the full influence of the Enlightener of the mind and Sanctifier of the heart. The reasons of this solemn asseveration are probably the following:
(1) His conduct and his doctrines had led some to believe that he was an apostate, and had lost his love for his countrymen. He had forsaken their institutions, and devoted himself to the salvation of the Gentiles. He here shows them that it was from no lack of love to them.
(2) The doctrines which he was about to state and defend were of a similar character; he was about to maintain that no small part of his own countrymen, notwithstanding their privileges, would be rejected and lost. In this solemn manner, therefore, he assures them that this doctrine had not been embraced because he did not love them, but because it was solemn, though most painful truth. He proceeds to enumerate their privileges as a people, and to show to them the strength and tenderness of his love.