WHEN POPE BENEDICT XVI went to Cologne, Germany, for World Youth Day in August 2005, many Germans expected the pope to take them to task on a variety of fronts-from declining Mass attendance and internal dissent within the Church, to a general unwillingness to grant religion a role in public life. Instead, Benedict offered a message that was at the same time more gentle and yet more radical. In his concluding homily, he chose to meditate on the Eucharist, Christ's gift of himself under the forms of bread and wine at Mass.

The pope offered a memorable metaphor to describe its impact. He told the one million young people who had gathered to hear him:

To use an image well known to us today, [consecrating the Eucharist] is like inducing nuclear fission in the very heart of being the victory of love over hatred, the victory of love over death, Only this intimate explosion of good conquering evil can then trigger off the series of transformations that little by little will change the world. All other changes remain superficial and cannot save. For this reason we speak of redemption: what had to happen at the most intimate level has indeed happened, and we can enter into its dynamic. Jesus can distribute his Body, because he truly gives himself.

That imagery came from Joseph Ratzinger's lifetime of prayer and devotion centered on the Eucharist.

In March 2007, Benedict XVI released a document called an "apostolic exhortation," officially drawing conclusions from the Synod of Bishops on the Eucharist that took place in the Vatican in October 2005. It's titled Sacramentum Caritatis (Sacrament of Charity) and it offers Benedict's most developed reflections on the Eucharist.

The Church's faith is essentiality a Eucharistic faith, and it is especially nourished at the table of the Eucharist....For this reason, the Sacrament of the Altar is always at the heart of the Church's life...The more lively the eucharistic faith of the People of God, the deeper is its sharing in ecclesial life in steadfast commitment to the mission entrusted by Christ to his disciples.

That last line is important, because as Benedict goes on to argue in Sacramentum Caritatis, the faith expressed in the Eucharist comes with a mission. On a personal level, it impels us to live our lives in accordance with what we profess during the Mass; we must become, as Saint Augustine once famously suggested, what we consume, meaning to model ourselves on Christ. On a social level, it means efforts to build a world in which the self-giving love of Christ, which is made new each time the Eucharist is celebrated, is the cornerstone upon which society is constructed, as opposed to ideology, profit, or the blind will to power.

Taken seriously, Benedict argues, the Eucharist can change the world-indeed, it's the only thing that can.