It is now four months since the drama of last April played itself out in slow motion and Pope John Paul left a world that was both bereaved and at the same time relieved that his agony was over. Even in death and beyond it he held the attention of the world until the cardinals elected a man from Germany, Josef Ratzinger, to the Papacy. Pope Benedict XVI took on the Cross.

It was apposite that his first participation in a World Youth Day should take place in Cologne. The idea for these gatherings began to germinate in Pope John Paul's mind in 1984 and were formalised on Palm Sunday in 1986. His biographer, George Weigel, saw the launch as "one of the signature initiatives of his pontificate": Buenos Aires in 1987, Santiago de Compostela in 1989, Czestochowa in 1991, Denver in 1993, Manila in 1995, Paris in 1997, Rome in 2000 and Toronto in 2002.

The signature now belongs to Pope Benedict who swiftly indicated how much he was looking forward to visit one of his country's cities dominated by that cascading mass of architecture, Cologne cathedral. Today will be an emotional moment for him, emotional and spiritual, culminating in an address to, and the Eucharistic celebration with, tens of thousands of young men and women. These started their pilgrimage to Cologne many days ago and have been waiting for this encounter with the rapture that goes so blessedly with youth.

What will he tell them? It is clear from the Wednesday audiences he has held at St Peter's Square, occasions when he takes his cue from spiritual texts to pronounce words of faith and encouragement, that in this encounter with youth he may well use as a base his belief that the evangelisation of the world needs, before all else, the evangelisation of youth.

In his first homily at the morning Mass after his election he spoke to the cardinals present of the need for "collegial communion... at the service of the Church and the unity of faith, from which depend in a notable measure the effectiveness of the evangelising action of the contemporary world". For, he may have added, if the salt loses its flavour wherein will it be salted? Pope Benedict may dwell on this today and on the urgency for that unity in a world that is making a religion of secularism and shows so many signs of faithlessness within the Church and outside it, in a world where so many find it intolerable to keep a promise, a vow, of fidelity.

The Pope let it be known early in his papacy that he will spend his energy in bringing about unity between the Orthodox and Christian Churches. He is deeply aware he is returning not merely to his home but to the home of the Reformation, which itself helped to bring about a Counter-Reformation that breathed new spiritual life into the Catholic Church. Differences remain between the Christian Churches, some of them seemingly irreconcilable, among them the ministry and sacramental aspects that are central to the identity and being of the Catholic Church.

There may be something providential about the Pope's first World Youth Day taking place in a country where thorny issues have long characterised these differences. What is certain is that Pope Benedict will not demolish them during this four-day trip that ends on Sunday. Many are hoping he will signal his readiness to engage in a dialogue that will strengthen unity, even if it is in diversity, without sacrificing integrity.

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