The inclusion of women in the rite is problematic for some because it could be seen as an opening of sorts to women's ordination. The Catholic Church restricts the priesthood to men, arguing that Jesus and his 12 apostles were male.
Francis is clearly opposed to women's ordination. But by washing the feet of women, he jolted traditionalists who for years have been unbending in insisting that the ritual is for men only and proudly holding up as evidence documentation from the Vatican's liturgy office saying so.
"If someone is washing the feet of any females ... he is in violation of the Holy Thursday rubrics," Peters wrote in a 2006 article that he reposted earlier this month on his blog.
In the face of the pope doing that very thing, Peters and many conservative and traditionalist commentators have found themselves trying to put the best face on a situation they clearly don't like yet can't do much about lest they be openly voicing dissent with the pope.
By Thursday evening, Peters was saying that Francis had merely "disregarded" the law — not violated it.
The Rev. John Zuhlsdorf, a traditionalist blogger who has never shied from picking fights with priests, bishops or cardinals when liturgical abuses are concerned, had to measure his comments when the purported abuser was the pope himself.
"Before liberals and traditionalists both have a spittle-flecked nutty, each for their own reasons, try to figure out what he is trying to do," Zuhlsdorf wrote in a conciliatory piece.
But, in characteristic form, he added: "What liberals forget in their present crowing is that even as Francis makes himself — and the church — more popular by projecting (a) compassionate image, he will simultaneously make it harder for them to criticize him when he reaffirms the doctrinal points they want him to overturn."
One of the key barometers of how traditionalists view Francis concerns his take on the pre-Vatican II Latin Mass. The Second Vatican Council, the 1962-65 meetings that brought the church into the modern world, allowed the celebration of the Mass in the vernacular rather than Latin. In the decades that followed, the so-called Tridentine Rite fell out of use almost entirely.
Traditionalist Catholics who were attached to the old rite blame many of the ills afflicting the Catholic Church today — a drop in priestly vocations, empty pews in Europe and beyond — on the liturgical abuses that they say have proliferated with the celebration of the new form of Mass.
In a bid to reach out to them, Benedict in 2007 relaxed restrictions on celebrating the old Latin Mass. The move was aimed also at reconciling with a group of schismatic traditionalists, the Society of St. Pius X, who split from Rome precisely over the Vatican II reforms, in particular its call for Mass in the vernacular and outreach to other religions, especially Judaism and Islam.
Benedict took extraordinary measures to bring the society back under Rome's wing during his pontificate, but negotiations stalled.
The society has understandably reacted coolly to Francis' election, reminding the pope that his namesake, St. Francis of Assisi, was told by Christ to go and "rebuild my church." For the society, that means rebuilding it in its own, pre-Vatican II vision.
The head of the society for South America, the Rev. Christian Bouchacourt, was less than generous in his assessment of Francis.
"He cultivates a militant humility, but can prove humiliating for the church," Bouchacourt said in a recent article, criticizing the "dilapidated" state of the clergy in Buenos Aires and the "disaster" of its seminary. "With him, we risk to see once again the Masses of Paul VI's pontificate, a far cry from Benedict XVI's efforts to restore to their honor the worthy liturgical ceremonies."
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