"breaking one and the same bread, which is the medicine of immortality, and the antidote which prevents us from dying, but a cleansing remedy driving away evil, [which causes] that we should live in God through Jesus Christ."
"You must not let anyone eat or drink of your Eucharist except those baptized in the Lord's name. For in reference to this the Lord said, "Do not give what is sacred to dogs."
Non-Christian whose writing
“They assert that this is the whole of their fault or error, that they were accustomed on a certain day to meet together before daybreak and to sing a hymn alternately to Christ as a god, and that they bound themselves by an oath (sacramento) not to do any crime, but only not to commit theft nor robbery nor adultery, not to break their word nor to refuse to give up a deposit. When they had done this, it was their custom to depart, but to meet again to eat food - ordinary and harmless food however.”
"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."
“But we, after we have thus washed him who has been convinced and has assented to our teaching, bring him to the place where those who are called brethren are assembled, in order that we may offer hearty prayers in common for ourselves and for the baptized person, and for all others in every place, that we may be counted worthy, now that we have learned the truth, by our works also to be found good citizens and keepers of the commandments, so that we may be saved with an everlasting salvation. Having ended the prayers, we salute one another with a kiss. There is then brought to the president (i.e. presiding Presbyter) of the brethren bread and a cup of wine mixed with water; and he taking them, gives praise and glory to the Father of the universe, through the name of the Son and of the Holy Ghost, and offers thanks at considerable length for our being counted worthy to receive these things at His hands. And when he has concluded the prayers and thanksgivings, all the people present express their assent by saying Amen. This word Amen answers in the Hebrew language to γένοιτο (so be it). And when the president has given thanks, and all the people have expressed their assent, those who are called by us deacons give to each of those present to partake of the bread and wine mixed with water over which the thanksgiving was pronounced, and to those who are absent they carry away a portion.”
For as the bread, which is produced from the earth, when it receives the invocation of God is no longer common bread, but the Eucharist, consisting of two realities, earthly and heavenly; so also our bodies, when they receive the Eucharist, are no longer corruptible, having the hope of the resurrection to eternity.
Wrote Anaphora, reconstructing early worship
"And we have a symbol of gratitude to God in the bread which we call the Eucharist"
Now, in your gatherings, in the holy Church, convene yourselves modestly in places of the brethren, as you will, in a manner pleasing and ordered with care. [So these “house liturgies” were NOT informal Masses. Good order and careful attention to detail were essential.] Let the place of the priests be separated in a part of the house that faces east. [So even in these early house Masses, the sanctuary (the place where the clergy ministered) was an area distinct from where the laity gathered. People were not all just gathered around a dining room table.] In the midst of them is placed the bishop’s chair, and with him let the priests be seated. Likewise, and in another section let the lay men be seated facing east. [Prayer was conducted facing east, not facing the people.] For thus it is proper: that the priests sit with the bishop in a part of the house to the east and after them the lay men and the lay women, [Notice that men and women sat in separate sections. This was traditional in many churches until rather recently, say the last 150 years.] and when you stand to pray, the ecclesial leaders rise first, and after them the lay men, and again, then the women. Now, you ought to face to east to pray for, as you know, scripture has it, Give praise to God who ascends above the highest heavens to the east. [Again, note that Mass was NOT celebrated facing the people as some suppose of the early Church. Everyone was to face to the east, both clergy and laypeople. Everyone faced in the same direction. The text cites Scripture as the reason for this. God is to the east, the origin of the light.]
Now, of the deacons, one always stands by the Eucharistic oblations and the others stand outside the door watching those who enter [Remember, this was a time of persecution and the early Christians were careful to allow only baptized and bona fide members to enter the Sacred Mysteries. No one was permitted to enter the Sacred Liturgy until after having been baptized. This was called the disciplina arcanis, or “discipline of the secret.” Deacons guarded the door to maintain this discipline.] and afterwards, when you offer let them together minister in the church. [Once the door was locked and the Mass began, it would seem that the deacons took their place in the sanctuary. However it also appears that one deacon remained outside the sanctuary to maintain “good order” among the laity.] And if there is one to be found who is not sitting in his place let the deacon who is within, rebuke him, and make him to rise and sit in his fitting place … also, in the church the young ones ought to sit separately, if there is a place, if not let them stand. Those of more advanced age should sit separately; the boys should sit separately or their fathers and mothers should take them and stand; and let the young girls sit separately, if there is really not a place, let them stand behind the women; let the young who are married and have little children stand separately, the older women and widows should sit separately. [This may all seem a bit complicated, but the bottom line is that seating was according to sex and age: the men on one side, the women on the other, older folks to the front, younger ones to the back. Also, those caring for young children were to stand in a separate area. See? Even in the old days there was a “cry room!”] And a deacon should see that each one who enters gets to his place, and that none of these sits in an inappropriate place. Likewise, the deacon ought to see that there are none who whisper or sleep or laugh or nod off. [Wait a minute! Do you mean to tell me that some of the early Christians did such things? Say it isn’t so! Today, ushers do this preserving of good order, but the need remains.] For in the Church it is necessary to have discipline, sober vigilance, and attentive ear to the Word of the Lord. [Well that is said pretty plainly—and the advice is still needed.]
St. Basil the Great, Archbishop of Caesarea of Cappadocia (died 379) on the basis of ancient church tradition, wrote the Divine Liturgy which now is celebrated 10 times a year by the Orthodox Church
St. John Chrysostom, Archbishop of Constantinopole (died 404) while not changing the essence of the Liturgy, shortened it, and in this form it is now celebrated in our churches on Sundays and week days throughout the year