What did the first Christians believe about the real presence of the actual body and blood of Jesus in the Eucharist?
Their opinion was unanimous:
Ignatius of Antioch
“I have no taste for corruptible food nor for the pleasures of this life. I desire the bread of God, which is the flesh of Jesus Christ, who was of the seed of David; and for drink I desire his blood, which is love incorruptible” (Letter to the Romans 7:3 [A.D. 110]).
“Take note of those who hold heterodox opinions on the grace of Jesus Christ which has come to us, and see how contrary their opinions are to the mind of God. . . . They abstain from the Eucharist and from prayer because they do not confess that the Eucharist is the flesh of our Savior Jesus Christ, flesh which suffered for our sins and which that Father, in his goodness, raised up again. They who deny the gift of God are perishing in their disputes” (Letter to the Smyrnaeans 6:2–7:1 [A.D. 110]).
“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” (First Apology 66 [A.D. 151]).
“If the Lord were from other than the Father, how could he rightly take bread, which is of the same creation as our own, and confess it to be his body and affirm that the mixture in the cup is his blood?” (Against Heresies 4:33–32 [A.D. 189]).
“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 receives the Word of God and becomes 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?” (ibid., 5:2).
Clement of Alexandria
“’Eat my flesh,’ [Jesus] says, ‘and drink my blood.’ The Lord supplies us with these intimate nutrients, he delivers over his flesh and pours out his blood, and nothing is lacking for the growth of his children” (The Instructor of Children 1:6:43:3 [A.D. 191]).
“[T]here is not a soul that can at all procure salvation, except it believe whilst it is in the flesh, so true is it that the flesh is the very condition on which salvation hinges. And since the soul is, in consequence of its salvation, chosen to the service of God, it is the flesh which actually renders it capable of such service. The flesh, indeed, is washed [in baptism], in order that the soul may be cleansed . . . the flesh is shadowed with the imposition of hands [in confirmation], that the soul also may be illuminated by the Spirit; the flesh feeds [in the Eucharist] on the body and blood of Christ, that the soul likewise may be filled with God” (The Resurrection of the Dead 8 [A.D. 210]).