Philip Schaff, on why “the greatest masters” in church history end up with an ever-expanding, universalizing vision of Christ and his church:
The ultra-Protestant fanatical opposition to the Catholic church must cease. The general disposition now is to break away from the narrow apologetic and polemic interest of a particular confession or party, the colored spectacles of which allow but a dim and partial view of the Saviour’s majestic person. We wish to be guided solely by the spirit of impartial truth; and truth, at the same time, always best vindicates itself by the simple exhibition of its substance and historical course. Christianity can never be absolutely fitted to the last of a fixed human formula, without losing her dignity and majesty; and her history may claim, for its own sake, to be thoroughly investigated and represented, sine ira et studio [“without anger or zeal”], without any impure or loveless designs. The greatest masters in this field become more and more convinced, that the boundless life of the church can never be exhausted by any single sect or period, but can be fully expressed only by the collective Christianity of all periods, nations, confessions, and individual believers; that the Lord has never left himself without a witness; that, consequently, ever period has its excellencies, and reflects, in its own way, the image of the Redeemer.
Newman famously (and incorrectly) said, “To be deep in history is to cease to be a Protestant.” Schaff might have replied: “To be deep in history is to cease to be sectarian and parochial.” That challenge cuts in all directions, implicating any narrow, polemical vision of the church—regardless of which communion you belong to.