My Aunt Mary, a staunch Baptist, loves having a nephew who's a priest.

At 70, and in spite of her arthritis, she insists on going to see me celebrate Mass when I'm home visiting my mom and dad. Before Mass, I normally remind her in a tactful way to refrain from receiving holy Communion.

There's never a problem. She understands. Yet not all Christians are like my aunt; not all understand or accept the Church's directive discouraging inter-communion. In fact, many Catholics and Protestants see nothing wrong with receiving communion in each other's churches. A few high-profile incidents confirm the practice of this belief.

For instance, back in 1998, President Bill Clinton, a Baptist, and his wife, Hillary, a Methodist, decided to receive Communion at the Regina Mundi Catholic Church in Johannesburg, South Africa. A spokesman for Clinton said the president had no regrets about receiving Communion. He understood that any baptized Christian could receive Communion. The late Cardinal John O'Connor, archbishop of New York at the time, kindly informed the president that his understanding was erroneous.

Then there's the case of British Prime Minister Tony Blair. Blair, an Anglican, until 1996 would take Communion with his wife, a Roman Catholic, while attending Mass. He stopped when Cardinal Basil Hume sent him a letter advising him not to do so. Saying he didn't mean to offend anyone, Blair promised not to receive C o m m u n i o n again but added: “I wonder what Jesus would have made of it?”

Not only do Protestants appear to be confused on the issue of inter-communion but some Catholics do as well.

Take the example of Mary McAleese, president of Ireland and former secretary of the Irish Catholic Bishops' Conference. As one of her first acts of office, she chose to receive communion at Christ Church Cathedral, an Anglican Church, in Dublin.

All of this raises two key questions: Where did the idea of Catholics and Protestants taking communion together come from? And why does the Catholic Church oppose it?

To answer the first question, we need to look at a popular Protestant practice called Eucharistic hospitality. This pastoral policy holds that any baptized person may receive communion in any Christian church. Many Christians, including some Catholics, like the sound of this.

The reason is evident: At first glance, it appears ecumenical.

Where's Corpus Christi unity?

Episcopalian pastor Samuel Lloyd III, rector of Trinity Church in Boston, agrees. “The understanding in the Episcopal tradition, and broadly among the more Protestant traditions,” he says, “is that the Eucharist is the family meal of the Christian community and all it takes to come to that meal is to be a baptized Christian.”

Eucharistic hospitality comes from a Protestant ecumenical theology. It downplays the importance of doctrine in favor of mutual pastoral concerns among Christians such as peace, social justice and environmental protection. In 1995, in an official visit to the Holy See, Konrad Raiser, general secretary of the World Council of Churches, stated to Pope John Paul II what the aim of ecumenism should be. He told the Pope that churches should abandon old theological disputes over dogma and unite to confront shared pastoral challenges.

In brief, Raiser argued that Christian unity should be understood not as a unity based on doctrine but based on what he calls a “unity as process.” In other words, pastoral pragmatism takes priority over Christian doctrine. Within this theological framework, Eucharistic hospitality, for many, makes perfect sense. Then why does the Catholic Church oppose it?

John Paul answers this question. In his encyclical letter Ecclesia de Eucharistia, released in April, he points out that the Eucharist “cannot be the starting point for communion [among Christians of different faiths].” Why? “Precisely because the Church's unity, which the Eucharist brings about through the Lord's sacrifice and communion in his body and blood, absolutely requires full communion in the bonds of the profession of faith, the sacraments and ecclesiastical governance.”

For this reason, the Pope says, “The Catholic faithful … while respecting the religious convictions of [their] separated brethren, must refrain from receiving the communion distributed in their celebrations, so as not to condone an ambiguity about the nature of the Eucharist and, consequently, to fail in their duty to bear witness to the truth.”

Put another way, for inter-communion to take place between Protestants and Catholics they should hold to the same truth about the Eucharist. On one hand, most Protestants see the bread and wine used for holy communion in their celebrations as mere external symbols of Jesus Christ. On the other hand, Catholics believe, in view of sacred Scripture and Tradition, that the bread and wine used for holy Communion in the Mass becomes after the consecration the very body and blood of Jesus Christ.

To dismiss these differences in favor of an inter-communion based on convenience rather than truth, in my judgment, would create a false unity.

The feast of Corpus Christi this year should remind Christians that Christ prayed at the Last Supper that we “may be one.” May our oneness come from the truth of Christ's body and blood of Christ in the holy Eucharist.

Legionary Father Andrew McNair

teaches at Mater Ecclesiae

in Wakefield, Rhode Island.