Very rarely do I believe that a human dialogue approaches its subject from two very different poles. However, in the case of Habermas and Ratzinger's dialogue, one could say that the subject of their talk (on secularization's dialectic with religion) is really the form of their interaction. These two authors come from two very different starting points with regard to the state, although no dialectic is undertaken without a uniting point, even if it is the midpoint between two very extreme poles.
Habermas' speech considers the possibility of there being a weight to those precursors to the constitution. Although he reaches out toward the possibility of such, one can tell that his thought is much more centered upon the self-referential rationality from which the ongoing nature of the state springs. However, his considerations also come upon the post-modern realization self-reflection of reason upon reason, admitting that there are proto-rational foundations to rationality, at least because such exist in the liberal society and hold weight. However, one can see his markedly post-Enlightenment mentality insofar as these questions hold much more weight for him with regard to addressing the rational situation in which society "derails" itself. He leaves the question open as to where these two are placed, which seems a bit overly self-referential but also appropriate for this short consideration.
The speech given by Cardinal Ratzinger (now Pope Benedict XVI) is perhaps a bit lighter and more open its presentation of questions for consideration. The theologian considers the relationship of the "poles" of reason and faith which forms each, making them intertwined in extra-referential dialogue which prevents pathologies in either. In addition, there is the unifying concept of "natural law" which has in many ways been rejected by the application of the scientific fact of evolution to philosophy in all forms (as well as the general development of Western relativism). Instead of offering a scholastic consideration of natural law, Ratzinger merely points toward the necessity of dialogue in which the participant parties will find those unifying points which are ultimately pre-political. In the end, his essay remains an open question regarding this mutual dialogue of faith and reason as well as general cross-cultural dialogue.
These two essays are an excellent set of "open paths" from which a variety of considerations and spring on the dialectics and dialogue in the secular world and how this process of dialogue relates to the foundational elements of the state. I highly recommend them as dense, important reflections.