The Protestant/Catholic divide in Germany lends an obvious ecumenical subtext to Benedict XVI's trip.

As a German theologian, and a convinced Augustinian, Joseph Ratzinger has long admired the Protestant Reformer Martin Luther. In 1965, commenting on the document Gaudium et Spes from the final session of the Second Vatican Council (1962-65), Ratzinger criticized the text for relying too much on the optimism of French Jesuit Teilhard de Chardin, and not enough on Luther's consciousness of the Cross and of sin. (Note that Ratzinger was complaining that a Catholic document neglected the father of the Protestant Reformation; that alone says something about his ecumenical attitudes).

Later, Ratzinger played a key role in rescuing an agreement with the Lutheran World Federation on the doctrine of justification. It was announced to much fanfare in June 1998, then seemingly unraveled, and rolled out again in June 1999. The heart of the agreement was this sentence: "By grace alone, in faith in Christ's saving work and not because of any merit on our part, we are accepted by God and receive the Holy Spirit, who renews our hearts while equipping us and calling us to good works."

When the agreement seemed to founder, German media reported that Ratzinger had torpedoed it. On July 14, 1998, Ratzinger published a letter in the German newspaper Frankfurter Allgemeine calling those reports a "smooth lie." He said that to scuttle the dialogue would be to "deny myself." On November 3, 1998, a special ad hoc working group met at the home of Ratzinger's brother Georg in Regensburg, Bavaria, to get the agreement back on track. Lutheran Bishop Johannes Hanselmann convened the group, which consisted of Hanselmann, Ratzinger, Catholic theologian Heinz Schuette and Lutheran theologian Joachim Track.

Given this background, coupled with the strong ecumenical commitment that has so far characterized Benedict's papacy, one would expect outreach during his German swing. The ecumenical meeting on the pope's program Friday evening at the archbishop's palace offers the ideal setting.

On the vexed issue of inter-communion between Catholics and Protestants, however, it would be naive to expect a sea change in Cologne.

The 1994 Catechism of the Catholic Church, issued under Ratzinger's authority as prefect for the Congregation for the Doctrine of the Faith, states that, "Ecclesial communities derived from the Reformation and separated from the Catholic Church have not preserved the proper reality of the Eucharistic mystery in its fullness, especially because of the absence of the sacrament of Holy Orders. It is for this reason that Eucharistic intercommunion is not possible for the Catholic Church."

This explains why Catholics can't take communion from a Protestant minister - from the Catholic point of view, that minister is not a properly ordained priest, and hence the communion is not a valid Eucharist.

On the other end, Protestants are generally not invited to the Catholic Eucharist because, again from the Catholic point of view, receiving the Eucharist implies unity in faith, and Catholics and Protestants have different beliefs about the Eucharist. (The 1993 Directory for the Application of Principles and Norms on Ecumenism, from the Pontifical Council for Christian Unity, lays out the conditions for individual exceptions).