Paul VI wrote an encyclical on the need for modern evangelization and in recent years we've heard much about the "New Evangelization" especially by John Paul II.
Interestingly, Pope Benedict plans to form a Pontifical Council for the New Evangelization to reinvigorate and in some places to reintroduce Catholicism in Europe and developed Western nations. Recall how the Catholic faith was first introduced to Ireland by missionaries where it thrived and then became the source of rekindling the faith in Europe. From where will the fire come this time?
Same place as before - The Holy Spirit.