"A church that took this step would cease to be the one, holy, catholic, and apostolic church."

     "Here lies the boundary of a Christian church that knows itself to be bound by the authority of Scripture.  Those who urge the church to change the norm of its teaching on this matter must know that they are promoting schism.  If a church were to let itself be pushed to the point where it ceased to treat homosexual activity as a departure from the biblical norm, and recognized homosexual unions as a personal partnership of love equivalent to marriage, such a church would stand no longer on biblical ground but against the unequivocal witness of Scripture.  A church that took this step would cease to be the one, holy, catholic, and apostolic church."

     Wolfhart Pannenberg, "Revelation and homosexual experience:  What Wolfhart Pannenberg says about this debate in the church," trans. Markus Bockmuehl, Christianity today 40, no. 13 (November 11, 1996):  35, 37.  ="Amor vincit omnia—or does it?  Outlook:  Homosexuality and scripture," trans. Markus Bockmuehl, Church times (June 21, 1996), modified by the above:

     Here lies the boundary of a Christian Church that knows itself to be bound by the authority of scripture.  Those who urge the Church to change the norm of its teaching on this matter must know that they are promoting schism.  If a Church were to let itself be pushed to the point where it ceased to treat homosexual activity as a departure from the biblical norm, and recognised homosexual unions as a personal partnership of love equivalent to marriage, such a Church would stand no longer on biblical ground but against the unequivocal witness of scripture. 

     A Church which took such a step would thereby have ceased to be one, holy, catholic, and apostolic.

="Maßstäbe zur kirchlichen Urteilsbildung über Homosexualität," in Beiträge zur Ethik (Göttingen:  Vandenhoeck & Ruprecht, 2004), 99-102.  ="'Einem männlichen Wesen darfst du nicht beiwohnen': Maßstäbe zur kirchlichen Urteilsbildung über Homosexualität," Zeitwende 65, no. 1 (1994): 1-4.  From the latter (the original, identical to the 2004 reprint), in which this does not begin a new paragraph, and which appeals to Luther rather than the four marks:

An dieser Stelle liegt die Grenze für eine christliche Kirche, die sich an die Autorität der Schrift gebunden weiß.  Wer die Kirche dazu drängt, die Norm ihrer Lehre in dieser Frage zu ändern, muß wissen, daß er die Spaltung der Kirche betreibt.  Denn eine Kirche, die sich dazu drängen ließe, homosexuelle Betätigung nicht mehr als Abweichung von der biblischen Norm zu behandeln und homosexuelle Lebensgemeinschaften als eine Form persönlicher Liebesgemeinschaft als eine Form persönlicher Liebesgemeinschaft neben der Ehe anzuerkennen, eine solche Kirche stünde nicht mehr auf dem Boden der Schrift, sondern im Gegensatz zu deren einmütigem Zeugnis.  Eine Kirche, die einen solchen Schritt tut, hätte darum aufgehört, evangelische Kirche in der Nachfolge der lutherischen Reformation zu sein.

. . . A church that takes such a step would have ceased to be [an] evangelical/Protestant church in the succession of the Lutheran Reformation.

 There is also at least one version of this up in German here.
     Cf. Yeago, Abraham, and others on this blog.  Abraham in another place:  "If the United Methodist Church were to abandon its current teaching on homosexual behavior, it would cease to be a body of congregations among which the pure Word of God is preached; and thus it would undermine its own most important ecclesiological insight" (William J. Abraham, "Chapter 1:  The Church’s teaching on sexuality:  a defense of the United Methodist Church’s Discipline on homosexuality," in Staying the course:  supporting the Church’s position on homosexuality, ed. Maxie D. Dunnam and H. Newton Malony (Nashville:  Abingdon Press, 2003), 30 (15-31)).