On the Holy Eucharist

151 AD: St. Justin Martyr

We call this food Eucharist, and no one else is permitted to partake of it, except one who believes our teaching to be true and who has been washed in the washing which is for the remission of sins and for regeneration [i.e., has received baptism] and is thereby living as Christ enjoined. For not as common bread nor common drink do we receive these, but since Jesus Christ our Savior was made incarnate by the word of God and had both flesh and blood for our salvation, so too, as we have been taught, the food which has been made into the Eucharist by the Eucharistic prayer set down by him, and by the change of which our blood and flesh is nurtured, is both the flesh and the blood of that incarnated Jesus.

180 AD:  St. Irenaeus of Lyons

So then, if the mixed cup and the manufactured bread receive the Word of God and become the Eucharist, that is to say, the Blood and Body of Christ, which fortify and build up the substance of our flesh, how can these people claim that the flesh is incapable of receiving God's gift of eternal life, when it is nourished by Christ's Blood and Body and is His member? As the blessed apostle says in his letter to the Ephesians, 'For we are members of His Body, of His flesh and of His bones' (Eph. 5:30). He is not talking about some kind of 'spiritual' and 'invisible' man, 'for a spirit does not have flesh an bones' (Lk. 24:39). No, he is talking of the organism possessed by a real human being, composed of flesh and nerves and bones. It is this which is nourished by the cup which is His Blood, and is fortified by the bread which is His Body. The stem of the vine takes root in the earth and eventually bears fruit, and 'the grain of wheat falls into the earth' (Jn. 12:24), dissolves, rises again, multiplied by the all-containing Spirit of God, and finally after skilled processing, is put to human use. These two then receive the Word of God and become the Eucharist, which is the Body and Blood of Christ.

He has declared the cup, a part of creation, to be his own blood, from which he causes our blood to flow; and the bread, a part of creation, he has established as his own body, from which he gives increase unto our bodies. When, therefore, the mixed cup [wine and water] and the baked bread receive the Word of God and become the Eucharist, the body of Christ, and from these the substance of our flesh is increased and supported, how can they say that the flesh is not capable of receiving the gift of God, which is eternal life — flesh which is nourished by the body and blood of the Lord and is in fact a member of him? 

350 AD:  St. Cyril of Jerusalem

The bread and the wine of the Eucharist before the holy invocation of the adorable Trinity were simple bread and wine, but the invocation having been made, the bread becomes the body of Christ and the wine the blood of Christ.

 
Do not, therefore, regard the bread and wine as simply that, for they are, according to the Master's declaration, the body and blood of Christ. Even though the senses suggest to you the other, let faith make you firm. Do not judge in this matter by taste, but be fully assured by faith, not doubting that you have been deemed worthy of the body and blood of Christ. . . [Since you are] fully convinced that the apparent bread is not bread, even though it is sensible to the taste, but the body of Christ, and that the apparent wine is not wine, even though the taste would have it so. . . partake of that bread as something spiritual, and put a cheerful face on your soul.

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