Adam Clarke on Galatians 3:5

He therefore that ministereth to you the Spirit - The apostle means himself: he had been the means of conveying the Holy Spirit to them, and by that Spirit he wrought miracles among them; and he did all this, not as a Jew, (for as such he had no power), but he did all as a believer in Christ. The word επιχορηγων, which we translate ministereth, is very emphatic, and signifies leading up the chorus, bringing up one after another, adding grace to grace, benefit to benefit; so that it appears that they had not only some, but many benefits; God, by means of his apostle, having greatly enriched them with various spiritual blessings.