"It was a splendid day on 11 October, 1962," Benedict wrote in a forward to a commemorative book about the anniversary published this week by the Vatican newspaper. "It was a moment of extraordinary expectation. Great things were about to happen."
Indeed, by its conclusion in 1965, the council had approved documents allowing for the celebration of Mass in the vernacular rather than Latin, and revolutionizing the church's relations with Jews, Muslims and people of other faiths.
Yet as great as that document on relations with other faiths was, Benedict wrote, a "weakness" has emerged in the ensuing years in that "it speaks of religion solely in a positive way and it disregards the sick and distorted forms of religion" that have become all too apparent.
Ratzinger was joined at Vatican II by another young theologian, Hans Kueng, who subsequently brought him to Tuebingen University in southern Germany as professor of dogmatic theology, helping promote an academic career that resulted in a papacy.
In the years since, Kueng has become one of Benedict's greatest critics, complaining that there has been no progress in reforming the church since Vatican II and calling for a grassroots revolt against the church hierarchy to carry it out.
"The council was unable to guarantee that the reforms would be implemented," primarily because the Vatican bureaucracy was and still is opposed, he said in an interview with German news website ntv-de this week.
Kueng, who lost his official license to teach Catholic theology but continues to teach, has opposed Benedict's outreach to traditionalist Catholics and his reintroduction of the old, pre-Vatican II Latin Mass.
"Ratzinger and his peers spiritually live in the Middle Ages," Kueng told n-tv.
A similar complaint was made recently by Cardinal Carlo Maria Martini, one of the last liberals in the College of Cardinals, who died Aug. 31. Martini was quoted as saying in his final interview that the church was in need of radical reform and was "200 years behind the times."
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