John Calvin on Galatians 2:8

8. He that wrought effectually. That the province which had been assigned to him was truly his own, is proved by the exertion of divine power during his ministry. Now, this manifestation of divine energy, as we have frequently seen, is the seal by which his doctrine was attested, and his office as a teacher sanctioned. Whether Paul refers God’s effectual working to the success of his preaching, or to the graces of the Holy Spirit which were then bestowed on believers, is doubtful. I do not understand it as denoting the mere success, but the spiritual power and efficacy, “La vertu et efficace spiriluelle.” which he has elsewhere mentioned. (1 Corinthians 2:4.) The amount of the whole is, that it was no idle bargain which the apostles had made among themselves, but a decision which God had sealed.