The perception of the spirituality of the law's demands may have been a great discovery, but a greater discovery remained to be made. Paul had yet to learn that the entire spirit in which he strove to fulfill the law, both inwardly and outwardly, the fundamental motive which inspired his pursuit of righteousness, was radically wrong because issuing from the flesh, the sinful determination of human nature which makes self instead of God supreme. There is no evidence that Paul made this discovery before the grace of God supernaturally illumined him at his conversion.
--“The Alleged Legalism in Paul’s Doctrine of Justification,” in Redemptive History and Biblical Interpretation: The Shorter Writings of Geerhardus Vos (ed. Richard B. Gaffin, Jr.; Phillipsburg, N.J.: Presbyterian & Reformed, 1980), 396.