Pope Benedict XVI on Tuesday reiterated the Church's ban on Communion for divorced Catholics who remarry and told Catholic politicians that the Vatican's stance against abortion and gay marriage is "not negotiable."

In a 131-page document, the pope also upheld the Vatican's requirement for celibacy for priests in the Latin rite Church. "Priestly celibacy lived with maturity, joy and dedication is an immense blessing for the Church and for society itself," the pope wrote.

The document embraced recommendations made by bishops from around the world at a 2005 meeting at the Vatican that rejected any change in the celibacy requirement. Benedict said bishops should "on no account" lower admission standards to seminaries to compensate for the shortage of clergy in some parts of the world.

"Certainly, a more equitable distribution of clergy would help to solve the problem," Benedict wrote, without being specific.

Last year, the pope led a Vatican summit on celibacy which rebuffed a challenge by an excommunicated African archbishop, Emmanuel Milingo, who is crusading for the Church to allow all priests to marry.

Benedict also acknowledged "the painful situations" of divorced Catholics who can no longer receive Communion after they remarry. The Catholic Church does not permit divorce and views such faithful as living in sin if they remarry and consummate their new marriages.

If efforts to annul the first marriages fail, and the couple continues to live together in their new marriage, "the Church encourages these members of the faithful to commit themselves to living their relationship ... as friends, as brother and sister," Benedict said. He was reiterating a stance held by his predecessor, John Paul II, that divorced Catholics who remarry cannot have sex with their new partners if they want to receive the Eucharist.

The question of whether Catholic politicians who support stands that conflict with Church teaching should be denied Communion gained attention during the 2004 U.S. presidential election campaign, when St. Louis Archbishop Raymond Burke said he would deny the Eucharist to Democratic presidential nominee John Kerry, a Catholic who was supporting abortion rights.

In the document, Benedict indicated that local bishops must deal with these cases.

Politicians must decide matters involving fundamental values, including respect for life "from conception to natural death, the family built upon marriage between a man and a woman, the freedom to educate one's children and the promotion of the common good in all its values," Benedict wrote.

"These values are not negotiable. Consequently Catholic politicians and legislators, conscious of their grave responsibility before society, must feel particularly bound, on the basis of a properly formed conscience, to introduce and support laws inspired by values grounded in human nature," Benedict wrote.

"There is an objective connection here with the Eucharist. Bishops are bound to reaffirm constantly these values as part of their responsibility to the flock entrusted to them," the pope said.

At a news conference to present the document, Venice Cardinal Angelo Scola was asked if the document meant that bishops should not give Communion to politicians who supported positions that contrast to Church teaching.

The cardinal declined to be specific in his answer, replying only that the document "doesn't say what it doesn't want to say."

Several times, Benedict struck what sounded like a nostalgic note for Mass before the reforms of the 1962-1965 Second Vatican Council, which included using local languages instead of Latin and inspired some congregations to introduce folk songs and other informal touches.

Seminarians should learn how to celebrate Mass in Latin, and faithful can be taught to recite the more common prayers in Latin, Benedict wrote.

Lately, on Wednesdays when the pope meets with thousands of pilgrims and tourists, the faithful have been invited to recite the Lord's Prayer in Latin, with the text printed in the audience's program.

"Certainly, as far as the liturgy is concerned, we cannot say that one song is as good as another," wrote Benedict, who likes to play classical piano music. "Generic improvisation or the introduction of musical genres which fail to respect the meaning of the liturgy should be avoided," Benedict said.

He added that he desired that the "Gregorian chant be suitably esteemed and employed" at Mass.