John Calvin on Galatians 5:7

7. Ye did run well. The censure which the apostle administers for their present departure from the truth is mingled with approbation of their former course, for the express purpose that, by being brought to a sense of shame, they may return more speedily to the right path. The astonishment conveyed in the question, who hindered you? was intended to produce a blush. I have chosen to translate the Greek word πείθσθαι, obey, rather than believe, because, having once embraced the purity of the gospel, they had been led away from a course of obedience.