Complex sentence: His book titled "Rediscovering Vatican II-Ecumenism and Interreligious Dialogue", published 2005, and marking the 40th Anniversary of the Vatican's ecumenism declaration Nostra Aetate, made a significant contribution to ongoing international inter-religious dialogue.
Split into simpler sentences: His book titled "Rediscovering Vatican II-Ecumenism and Interreligious Dialogue", was published 2005 and marked the 40th anniversary of the Vatican's ecumenism declaration "Nostra Aetate". The book made a significant contribution to ongoing international inter-religious dialogue.