Here's what the U.S. Conference of Catholic Bishops (USCCB) says about the topic for non-Catholic Christians:We welcome our fellow Christians to this celebration of the Eucharist as our brothers and sisters. We pray that our common baptism and the action of the Holy Spirit in this Eucharist will draw us closer to one another and begin to dispel the sad divisions which separate us. We pray that these will lessen and finally disappear, in keeping with Christ's prayer for us "that they may all be one" (Jn 17:21).
Because Catholics believe that the celebration of the Eucharist is a sign of the reality of the oneness of faith, life, and worship, members of those churches with whom we are not yet fully united are ordinarily not admitted to Holy Communion. Eucharistic sharing in exceptional circumstances by other Christians requires permission according to the directives of the diocesan bishop and the provisions of canon law (
canon 844 §4). Members of the Orthodox Churches, the Assyrian Church of the East, and the Polish National Catholic Church are urged to respect the discipline of their own Churches. According to Roman Catholic discipline, the Code of Canon Law does not object to the reception of Communion by Christians of these Churches (
canon 844 §3).
and adds for non-Christians:We also welcome to this celebration those who do not share our faith in Jesus Christ. While we cannot admit them to Holy Communion, we ask them to offer their prayers for the peace and the unity of the human family.
The above excerpts are printed in missalettes everywhere and may be read in full on the USCCB site at http://www.usccb.org/prayer-and-worship/the-mass/order-of-mass/liturgy-of-the-eucharist/guidelines-for-the-reception-of-communion.cfm. There is also a very thorough treatment on the sacramentality and importance for unity of the Eucharist in the Catechism of the Catholic Church at http://www.vatican.va/archive/ccc_css/archive/catechism/p2s2c1a3.htmAs Catholics we believe that the Eucharist, the "fount and apex [source and summit] of Christian life" (
Lumen Gentium 11) is the most concrete sign that we have of the reality of our unity in faith, worship and life in Christ. Scripture itself is very clear that partaking of the Eucharist is among the highest signs of Christian unity: "Because there is one bread, we who are many are one body, for we all partake of the one bread" (1 Cor. 10:17).
When we say "Amen", in response to "The Body of Christ", "The Blood of Christ", we are saying that we believe that what the minister holds before us - the consecrated Bread and wine - are really and truly the Body and Blood of Christ as the Church intends. For this reason, it is normally impossible for those outside of the Catholic Church to receive Holy Communion, for to do so would be to proclaim a unity to exist that, regrettably, does not.
But it is certainly one that we should constantly pray and work to one day bring about.