“The significance of the Theses as a Reformation act emerges thus in this: that they are a bold, an astonishingly bold, and a powerful, an astonishingly powerful, assertion of the evangelical doctrine of salvation, embodied in a searching, well-compacted, and thoroughly wrought-out refutation of the sacerdotal conception, as the underlying foundation on which the edifice of the indulgence-traffic was raised.... The matter would be better expressed, however, by saying that Luther here sets the evangelical principle flatly in opposition to the sacerdotal. What he here attacks is just the sacerdotal principle in one of its most portentous embodiments—the teaching that men are to look to the Church as the institute of salvation for all their souls’ welfare, and to derive from the Church all their confidence in life and in death. What he sets over against this sacerdotalism is the evangelical principle that man is dependent for his salvation on God and on God alone—on God directly, apart from all human intermediation—and is to look to God for and to derive from God immediately all that makes for his soul’s welfare. In these Theses Luther brought out of the academic circle in which he had hitherto moved, and cast into the arena of the wide world’s conflicts, under circumstances which attracted and held the attention of men, his newly found evangelical principle, thrown out into sharp contrast with the established sacerdotalism. It is this that made the posting of these Theses the first act of the Reformation, and has rightly made October Thirty-first the birthday of the Reformation.” — B.B. Warfield, The Ninety-Five Theses in Their Theological Significance (1917)