"What counts in the Church is not progress but reformation"

     "Conversely, it is not the newness, the modernity, the up-to-dateness of a Church which as such proves and commends it as the true and catholic Church. . . .  modernity, up-to-dateness, has nothing whatever to do with the question of the truth of the Church. For that reason the idea of progress is a highly doubtful one as applied to the Church. What counts in the Church is not progress but reformation—its existence as ecclesia semper reformanda. Semper reformari, however, does not mean always to go with the time, to let the current spirit of the age be the judge of what is true and false, but in every age, and in controversy with the spirit of the age, to ask concerning the form and doctrine and order and ministry which is in accordance with the unalterable essence of the Church. It means to carry out to-day better than yesterday the Christian community's one task which needs no revision, and in this way to 'sing unto the Lord a new song.' It means never to grow tired of returning not to the origin in time but to the origin in substance of the community. The Church is catholic when it is engaged in this semper reformari, so that catholicism has nothing to do with conservatism either, but very much to do with the sound common sense of the prayer of the robust Nicholas Selnecker (which is still to be found even in the new Swiss hymnbook): 'Against proud spirits stand and, fight, / Who lift themselves in lofty might, / And always bring in something new, / To falsify thy teaching true.' Therefore neither flirtation with the old nor flirtation with the new makes the Church the true Church, but a calm consideration of that which as its abiding possession is superior to every yesterday and to-day and is therefore the criterion of its catholicity."

     Karl Barth, CD IV/1, 704-705 =KD IV, 787.  Those Selnecker lines in German:  "Den stolzen Geistern wehre doch, | die sich mit G'walt erheben hoch | und bringen stets was Neues her, | zu fälschen deine rechte Lehr'!"
     For much more, go here.