The usual combination of penetrating psychological awareness/theological profundity, on the one hand, with recognition of the crucial social/ethnic questions of first-century Christianity on the other:
The mainspring of the controversy was not national interests or ecclesiastical ambition, but the central question: What does God require of man and how can man be justified before God?
. . . Now the union between Church and Jewry was Paul's ultimate hope. . . . He looked upon the breach between the Church and the Jewish people with deep sorrow and knew better than anyone what a great hindrance it was even to his work among the gentiles. But he brushed aside all ecclesiastical and national considerations. . . . He was solely concerned with the purely religious aspect of the matter in its deepest sense. As he saw it, his opponents had altered the substance of the Gospel by repudiating what had been accomplished by the Cross of Christ.
. . . The God who acted in Jesus was not a God who commands and demands, but a God who gives. Hence Christian piety involved the resolute rejection of every human claim to merit, and an equally resolute acceptance of reconciliation with God. These were the aims which made Paul enter the fray with might and main.
--Adolf Schlatter, The Church in the New Testament Period (1926), 169-71; emphasis original