There are but Paul and Peter who name their apostleship at the beginning of their Epistles; and Paul, in supposing the Epistle to the Hebrews to be his, which I do not doubt, does not call himself so there. This title is not found in Philippians, and 2 Thessalonians, or Philemon. The character of these Epistles is much more personally fraternal. (He associates also others, but this is not by itself an absolute reason.) But these facts show the title is assumed with a definite purpose and meaning—Paul and Barnabas, and, in result, Paul having mission to the Gentiles, and Peter to the Jews, assume their title when in special exercise of their mission. The others write according to the wisdom and gift of God. This is the case with Paul in the Hebrews, for he had not the place of Apostle with them, and the kind of intercourse with the Thessalonians and Philemon, instead of claiming such a title, rendered it unsuited to the occasion. It was not authoritative revelations, or mandates, or the assumption of this place, as title and ground of intercourse, but brotherly occasions of tender care or thankful communication. Though the truth he might announce might be the same, and its authority equal, in the cases in which it is used its proper bearing is evident.
He had never seen the Romans, and he was to present himself as the called Apostle of all the Gentiles. Among the Corinthians, he had to exercise this authority to put things in order, and an authority contested. In the Galatians, it was the question in a great measure, though because of the truths which he taught. In Ephesians and Colossians, he is in a definite way the depositary of the great mystery of the Church, as Apostle of the Gentiles, and of Christ in them the hope of glory. The position of Timothy and Titus who were to regulate important things in virtue of his authority make the use of this title evident and clear. Hence the use of it in a revealed Epistle is not to be looked for without a reason, and, generally speaking, Peter and Paul alone are in this place in respect of their scriptural relationships with the Church. The authority does not come simply from Apostleship, but from the will of God acting by inspiration. The manner of address is connected with the bearing of the letter, though that be an instruction for all times, for it is in these circumstances that the ways of God in the Church are fully developed, and the proper Christian relationships, as well as divine truths, unfolded.