Was St Paul’s thought consistent? It can hardly be denied that the Apostle makes statements in his various epistles that appear to be in tension (or, some cases, even to flatly contradict) one another. Not a few scholars argue on the these grounds that it is impossible to read St Paul’s writings as a coherent corpus—with some, to borrow Moisés Silva’s words, raising questions “not just about the authority of apostolic teaching but about Paul’s basic intelligence.” But of course, this need not be so, as a sympathetic reading of the Pauline epistles readily demonstrates. Machen addresses the point as it relates to the claims of independence that St Paul makes for “his Gospel” in the Epistle to the Galatians, and concludes that far from being an impossibility, reading St Paul’s epistles as a coherent whole is necessary if we wish to avoid a myopic reading of these texts.
” . . . 2 Cor. v. 16, rightly interpreted, does not attest any indifference on the part of Paul toward the information about Jesus which came to him through contact with Jesus disciples. Such indifference, however, is also thought to be attested by the Epistle to the Galatians. In Gal. i, ii, Paul emphasizes his complete independence over against the original disciples. He received his gospel, he says, not by the instrumentality of men, but by direct revelation from the risen Christ. Even after the revelation he felt no need of instruction from those who had been apostles before him. It was three years before he saw any of them, and then he was with Peter only fifteen days. Even when he did finally have a conference with the original apostles, he received nothing from them; they recognized that God had already entrusted him with his gospel and that they had nothing to add. What can this passage mean, it is asked, except that Paul was indifferent to tradition, and derived his knowledge of Christ entirely from revelation?
“In answer, it is sufficient to point to 1 Cor. xv. 1-11. Was Paul indifferent to tradition? In 1 Cor. xv. 3 he himself attests the contrary; he places tradition—something that he had received—at the very foundation of his missionary preaching. “For I delivered unto you among the first things,” he says, “that which I also received.” The word “received” here certainly designates information obtained by ordinary word of mouth, not direct revelation from the risen Christ; and the content of what was “received” fixes the source of the information pretty definitely in the fifteen days which Paul spent with Peter at Jerusalem. It is almost universally admitted that 1 Cor. xv. 3ff. contains the tradition of the Jerusalem Church with regard to the death and resurrection of Jesus.
“The comparison with 1 Cor. xv. 1-11 thus exhibits the danger of interpreting the Epistle to the Galatians in one-sided fashion. If Galatians stood by itself, the reader might suppose that at least the resurrection of Christ, the central fact of Paul’s gospel, was founded, in Paul’s preaching, upon Paul’s own testimony alone. In Galatians Paul says that his gospel was not derived from men. But his gospel was grounded upon the resurrection of Christ. Surely, it might be said, therefore, he based at least the resurrection not at all upon the testimony of others but upon the revelation which came to him from Christ. Is it possible to conceive of the author of Galatians as appealing for the foundation of his gospel to the testimony of Peter and the twelve and other brethren in the primitive Church—to the testimony of exactly those men whose mediatorship he is excluding in Galatians? Yet as a matter of fact, that is exactly what Paul did. That he did so is attested not by the Book of Acts or by any source upon which doubt might be cast, but by one of the accepted epistles. The Epistle to the Galatians must always be interpreted in the light of 1 Cor. xv. 1-11.”
(J. Gresham Machen, The Origin of Paul’s Religion [1925; reprint, Grand Rapids: Eerdmans, 1973], pages 144-145.)
Also, for a masterful elucidation of whether St. Paul was a systematic thinker, see Moisés Silva, “Systematic Theology and the Apostle to the Gentiles” (Trinity Journal 15.1 :3-26), available online at the link, and in a reworked format as chapter 8 of Interpreting Galatians: Explorations in Exegetical Method (2nd ed.; Grand Rapids: Baker, 2001).