Pope John Paul II issued a stern reminder Thursday that only priests can celebrate Mass and divorced Catholics who remarry cannot take communion, expressing alarm over what he called unacceptable practices in his flock.
John Paul also warned Catholics against receiving communion in non-Catholic churches, an admonition that is likely to stir up protests in the United States and other countries where interfaith services are a fundamental part of efforts to bring Christians closer together.
Some Protestant officials immediately criticized the warnings as a step backward in efforts to achieve Christian unity.
The pope's denunciations of practices clashing with Vatican teaching were contained in an encyclical issued on Holy Thursday, a commemoration of Jesus' Last Supper with his apostles.
The 78-page document is aimed at combatting abuses related to the Eucharist, commonly called communion, a sacrament central to the life of the Church.
"It is my hope that the present encyclical letter will effectively help to banish the dark clouds of unacceptable doctrine and practice," the pope wrote.
"In various parts of the Church abuses have occurred, leading to confusion with regard to sound faith and Catholic doctrine concerning this wonderful sacrament."
In parts of Western Europe, as well as in the United States, many divorced Catholics who have remarried have been clamoring for the Church to allow them to receive communion.
But John Paul cited centuries-old teaching that all faithful must confess grave sins before taking communion.
"The judgment of one's state of grace obviously belongs only to the person involved, since it is a question of examining one's conscience," the pope said.
"However, in cases of outward conduct, which is seriously, clearly and steadfastly contrary to the moral norm, the Church, in her pastoral concern for the good order of the community and out of respect for the sacrament, cannot fail to feel directly involved," wrote John Paul.
He reiterated Church law that those who "obstinately persist in manifest grave sin" be denied communion.
The Vatican does not permit divorce and teaches that those who remarry after divorce are living in sin unless couples refrain from sex.
While the pope didn't name any sins, his reference to divorce was unmistakable since the Church considers remarried Catholics living in a state of continued sin, and experts said his intent was clear.
"That is what the Vatican is saying for years about the non-admission of public sinners to the Eucharist whether they be divorced or Mafia or people who are notorious criminals," said the Rev. Thomas Reese, editor of America, a Jesuit magazine.
The pontiff is "articulating a general principle of not admitting public sinners to the Eucharist, while not necessarily getting into the details of each person's life," said Reese, based in New York.
John Paul also expressed concern about parishes that are without priests. But while he said it was "praiseworthy" that nuns or laity in these communities lead the other faithful in prayer, only priests can celebrate Mass.
The pope also warned against loose interpretations by those hoping to foster closer relations among various Christian denominations.
Specifically, he ruled out as "unthinkable" the practice of substituting obligatory Sunday Mass with celebrations of prayer with Christians from other faiths "or even participation in their own liturgical services."
John Paul expressed dismay that sometimes the Eucharist "is celebrated as if it were simply a fraternal banquet."
He also wrote that Catholics "while respecting the religious convictions of these separated brethren, must refrain from receiving the communion distributed in their celebrations."
Roman Catholics maintain that they receive the blood and body of Christ in communion, but many other Christians view communion as a symbolic re-creation of the Last Supper.
Many Protestants believe that sharing in communion can help bring about unity.
But the pope wrote that "it is not possible to celebrate together the same Eucharist liturgy until those bonds are fully re-established."
John Paul said, however, that under special circumstances, communion can be given to Christians outside the Catholic church to meet "a grave spiritual need for the eternal salvation of an individual believer," and that in similar special circumstances, Catholics could ask that communion, confession or final rites be given by ministers from other faiths that also have "valid" sacraments.
The archbishop of Canterbury, Rowan Williams, said he welcomed "the pope's reaffirmation of his 'burning desire' for common Eucharistic celebration. This is an area of work which continues to be important for relations between Anglicans and Roman Catholics and we continue to work theologically on this."
But in Italy, where Protestants are a tiny minority, Domenico Tomassetto, a member of the ecumenical relations commission of the Baptist, Waldensian and Methodist churches in Italy, attacked the encyclical as making "a definite cut to the entire ecumenical process."