Paul makes no doubt that the Jewish Apostle's experience of salvation corresponded with his own. Doubtless, in their previous intercourse, and especially when he first "made acquaintance with Cephas" (ch. i. 18) in Jerusalem, the hearts of the two men had been opened to each other; and they had found that, although brought to the knowledge of the truth in different ways, yet in the essence of the matter--in respect of the personal conviction of sin, in the yielding up of self-righteousness and native pride, in the abandonment of every prop and trust but Jesus Christ--their history had run the same course, and face answered to face. Yes, Paul knew that he had an ally in the heart of his friend. He was not fighting as one that beateth the air, not making a rhetorical flourish, or a parade of some favourite doctrine of his own; he appealed from Peter dissembling to Peter faithful and consistent. Peter's dissimulation was a return to the Judaic ground of legal righteousness. By refusing to eat with uncircumcised men, he affirmed implicitly that, though believers in Christ, they were still to him "common and unclean," that the Mosaic rites imparted a higher sanctity than the righteousness of faith. Now the principles of evangelical and legal righteousness, of salvation by faith and by law-works, are diametrically opposed. It is logically impossible to maintain both. Peter had long ago accepted the former doctrine. He had sought salvation, just like any Gentile sinner, on the common ground of human guilt, and with a faith that renounced every consideration of Jewish privilege and legal performance. By what right can any Hebrew believer in Christ, after this, set himself above his Gentile brother, or presume to be by virtue of his circumcision and ritual law-keeping a holier man? Such we take to be the import of Paul's challenge in vv. 15, 16. III. Paul is met at this point by the stock objection to the doctrine of salvation by faith--an objection brought forward in the dispute at Antioch not, we should imagine, by Peter himself, but by the Judaistic advocates. _To renounce legal righteousness was in effect_, they urged, _to promote sin--nay, to make Christ Himself a minister of sin_ (ver. 17). Paul retorts the charge on those who make it. _They promote sin_, he declares, _who set up legal righteousness again_ (ver. 18). The objection is stated and met in the form of question and answer, as in Rom. iii. 5. We have in this sharp thrust and parry an example of the sort of fence which Paul must often have carried on in his discussions with Jewish opponents on these questions.