The Fathers on Closed Communion of the Eucharist

The Orthodox practice of allowing only those who are Baptized and Chrismated members of the Church to partake of the Eucharist is an ancient one.

"But let no one eat or drink of this Eucharistic thanksgiving, but they that have been baptized into the name of the Lord; for concerning this also the Lord hath said: 'Give not that which is holy to the dogs.'" - Didache, 9, 10-12 (AD 60)

"And this food is called among us the Eucharist, of which no one is allowed to partake but the man who believes that the things which we teach are true, and who has been washed with the washing that is for the remission of sins, and unto regeneration, and who is so living as Christ has enjoined. For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh by the Word of God, had both flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh." - St. Justin Martyr, First Apology, 66 (AD 150)

"And when a certain one, who himself was defiled, dared with the rest to receive secretly a part of the sacrifice celebrated by the priest; he could not eat nor handle the holy of the Lord, but found in his hands when opened that he had a cinder. Thus by the experience of one it was shown that the Lord withdraws when He is denied; nor does that which is received benefit the undeserving for salvation, since saving grace is changed by the departure of the sanctity into a cinder." - St. Cyprian of Carthage, On the Lapsed, 26 (AD 254)

"His poverty enriches, the fringe of His garment heals, His hunger satisfies, His death gives life, His burial gives resurrection. Therefore, He is a rich treasure, for His bread is rich. And 'rich' is apt for one who has eaten this bread will be unable to feel hunger. He gave it to the Apostles to distribute to a believing people, and today He gives it to us, for He, as a priest, daily consecrates it with His own words. Therefore, this bread has become the food of the saints." - St. Ambrose of Milan, On the Patriarchs, 9, 38 (AD 390)