"What makes the Church the Church, accordingly, are those elements that do not derive from merely human activity. They alone distinguish the Church from all other communal groupings and accord her the quality of being unique, being irreplaceable. Division within the Church thus consists of a split in the confession of faith, the creed, and the administration of the sacraments themselves; all other differences do not ultimately count: there can be no objection to them; they do not divide us in the heart of the Church. Division within the central sphere, on the other hand, threatens the very real reason for the Church's existence, her very being.
From this basic understanding of unity arose two tasks for ecumenism. It had first of all to distinguish purely human divisions from the real theological divides. Purely human divisions, in particular, like to give themselves the importance of something essential; they hide themselves, so to speak, behind this: what is human, what we have made for ourselves, is declared obligatory, as being divine. The silent divinization of what is our own, which is the everlasting temptation for man, easily spreads. In a high proportion of church schisms, such divinizing of what is ours, the self-assertion of some human or cultural form, has played a significant role. Ecumenism demanded, and still demands, the attempt to free ourselves from which distortions, which are often subtle. Then it follows that the variety by no means needs to disappear, because it does not detract from the nature of the Church; this can be special in some way and that can be different, but these things do not have to compulsory for everyone. A tolerance for different things had to arroused, not founded on indifference concerning the truth, but on the distinction between truth and mere human tradition." [Pilgrim Fellowship of Faith, p. 255]
Thus far Benedict XVI. What I find very interesting in his observation here is that it is this precise distinction which the Lutherans sought to make during the Reformation. Why, it could be taken as a paraphrase of AC VII almost! Our Churches saw, for example, in the elevation of the post-Biblical distinction between presbyter and episcopus to the status of a divinely instituted order upon which the very existence of the Church's sacramental life was built exactly the dangerous divinization of what was, in point of fact, merely human. Our Churches were all for keeping canonical order, of course, [sadly historical circumstance prevented this] but as a human tradition, not as something laid down for us in the "faith once delivered to the saints." This explains why there are Lutheran Churches with episcopal succession and Lutheran churches without it in complete Eucharistic fellowship. To us, it can never be more than a venerable human tradition. There were other examples, but that one comes to mind given the discussion under the other quote from Benedict.