Mahlmann, quoting Dittmer, on the phrase ecclesia semper reformanda

The traditional dichotomous division . . . of [the] church into [a] spiritual community (inward, eccl[esia] abscondita, proprie, community of believers) on the one hand, and [a] bodily community (outward, eccl[esia] visibilis, improprie, community of the baptized) on the other, must . . . be extended out into a trichotomously articulated concept of the church (I-III).  According to this [conception] it is (I) its pneumatic foundation ([the] opus Dei [(work of God)] that establishes the church as [a] spiritual community.  Within the sphere of the church as traditional so-called bodily community one must distinguish further between the dimension of [the] bodily community as (II) concept or typically ideal way of speaking or regulative idea, and th[at] dimension of the] bodily community as (III) [that] historical reality to which ecclesia semper reformanda est applies.   While the four classical notae internae or essential properties of the church (one, holy, catholic, and apostolic) are applicable to level I, the two reformed characteristics or notae externae (Word and Sacrament as means of grace; cf. CA 7) are to be applied to level II.

     "According to [the systematic theologian Johannes M.] Dittmer, ecclesia semper reformanda can therefore be applied exclusively to aspect of the 'church' no. III, and has therefore a narrow significance.  The call [for perpetual reform issued by] the formula can never [1] touch upon aspect of the 'church' no. II—that is its mission [(Auftrag)], the 'administration of the means of grace instituted by God' (CA 5, 7, and 8), to put it in the ancient phraseology [quite] deliberately—[2] dispense with it, or even [3] want only to alter ([i.e.] improve upon) it.  And certainly not aspect no. I of the 'church', for this is, as worked [(gewirkt)] by the means of grace (aspect II of the ‘church’ no. II), the opus Dei solius [(work of God alone).  But] in order that this might be grasped even more precisely, I propose to tease out of aspect of the 'church' no. III, in the sense of the optimal, an aspect no. IV in the sense of the deficient historical accomplishment of its task, and to relate ecclesia semper reformanda only to this aspect of the 'church' no. IV.  Every understanding of the formula that goes beyond this narrow significance is illegitimate, since this—to put it with Balthasar Mentzer (1565-1627)—[would be to] destroy 'die gantze Ordnung vnsers Heyls | und alle die Mittel | welche Gott zu vnser Seligkeit verordnet hat [(the entire order of our salvation | and all the means | that God has established for our beatitude)]'."

     Theodor Mahlmann, "'Ecclesia semper reformanda': eine historische Aufklärung: neue Bearbeitung," in Hermeneutica sacra: Studien zur Auslegung der Heiligen Schrift im 16. und 17. Jahrhundert:  Bengt Hägglund zum 90. Geburtstag, ed. Torbjörn Johansson, Robert Kolb, and Johann Anselm Steiger, Historia hermeneutica:  Series studia 9 (Berlin:  Walter de Gruyter, 2010), 383 (381-442).
     For much more, go here.