From "The Word"
Kimisis Tis Theotokou, Poughkeepsie
Rev. Father Nicholas Pastrikos, Pastor
Question: Should an Orthodox Christian receive communion in a Catholic church or become a sponsor in a non-Orthodox church?
The answer is "NO." It is important to understand why the answer is "NO." The sacrament of communion and every Orthodox sacrament is the primary and chief way that we as Orthodox Christians experience and manifest our unity and our purity within the Church. In the canon law practice of the Church, Christians are prohibited from receiving communion until they show signs of repentance over a period time, when they have committed a serious sin.
Also, those who break communion with the Church by marrying outside the Orthodox Church (that is in a civil ceremony, or another Church) are not permitted to receive communion or any of the Orthodox sacraments until their marriage is blessed in the Orthodox Church. Receiving communion is a sign and expression of a person's membership in the Church. To receive communion in another Church, or to become a sponsor in another Church is essentially to try to declare oneself a member of two different kinds of churches each with a different faith, worship, leadership, canon, moral principles etc. As you can see, it is a contradiction which creates confusion and in fact, impossible to do with full commitment and honesty.
Daniel the Stylite of Constantinople; Luke the New Stylite of Chalcedon; Holy Martyrs Ascepsia and Aethal; Holy Martyrs Miracus and Barsabas; Leontios the Righteous of Monemvasia; The Glorious King Nikephoros Phokas