communion lies “at the heart of the Church’s selfunderstanding”4, insofar as it is the Mystery of the personal union of each human being with the divine Trinity and with the rest of mankind, initiated with the faith5, and, having begun as a reality in the Church on earth, is directed towards its eschatological fulfilment in the heavenly Church6. If the concept of communion, which is not a univocal concept, is to serve as a key to ecclesiology, it has to be understood within the teaching of the