Petra and Skandalon
We have grown accustomed to make a clear distinction between Peter the rock and Peter the denier of Christ -- the denier of Christ: that is the Peter as he was before Easter; the rock: that is the Peter as he was after the Pentecost, the Peter of whom we have constructed a singularly idealistic image.
But, in reality, he was at times both of these... Has it not been thus throughout the history of the Church that the Pope, the successor of Peter has been at once Petra and Skandalon -- both the rock of God and a stumbling-block?
In fact the faithful will always have to reckon with this paradox of the divine dispensation that shames their pride again and again.
~ Pope Benedict XVI, Das neue Volk Gottes, pp 80ff.