The Constant teaching of the Church
Individuals can make mistakes or misunderstand their teachers BUT the fact that we find a continuous and unbroken chain of believing in the real presence of our Lord in the Eucharist is extremely strong evidence that this belief was in existence from the very first moments of Christian history.
I mean, a follower of Jesus could reject what He taught but the others who were taught directly by Jesus would not teach the same error.
Let’s go back through time to find what Christians believed on the Real Presence. In our Catechism, the official teaching of the Church on the Eucharist, we find: the catechism quoting the council of Trent from 1551 that the belief in the real presence to have been at least from 1551 to today:
1376 The Council of Trent summarizes the Catholic faith by declaring: "Because Christ our Redeemer said that it was truly his body that he was offering under the species of bread, it has always been the conviction of the Church of God, and this holy Council now declares again , that by the consecration of the bread and wine there takes place a change of the whole substance of the bread into the substance of the body of Christ our Lord and of the whole substance of the wine into the substance of his blood. This change the holy Catholic Church has fittingly and properly called transubstantiation."
The Reformation brought on the need for the Council of Trent because many started teaching contrary to the Church on many matters including the Real Presence. But what about before that time?
Council of Ephesus
"We will necessarily add this also. Proclaiming the death, according to the flesh, of the only-begotten Son of God, that is Jesus Christ, confessing his resurrection from the dead, and his ascension into heaven, we offer the unbloody sacrifice in the churches, and so go on to the mystical thanksgivings, and are sanctified, having received his holy flesh and the precious blood of Christ the Savior of us all. And not as common flesh do we receive it; God forbid: nor as of a man sanctified and associated with the Word according to the unity of worth, or as having a divine indwelling, but as truly the life-giving and very flesh of the Word himself. For he is the life according to his nature as God, and when he became united to his flesh, he made it also to be life-giving" (Session 1, Letter of Cyril to Nestorius [A.D. 431]).
"[Christ] took the bread and the cup, each in a similar fashion, and said: 'This is My Body and this is My Blood.' Not a figure of His body nor a figure of His blood, as some persons of petrified mind are wont to rhapsodize, but in truth the Body and the Blood of Christ." (Marcus the Magnesian)
c. 370 AD
"You ought to know what you have received, what you are going to receive, and what you ought to receive daily. That Bread which you see on the altar, having been sanctified by the word of God, is the Body of Christ. The chalice, or rather, what is in that chalice, having been sanctified by the word of God, is the Blood of Christ. " (St Augustine)
Council of Nicaea I
"It has come to the knowledge of the holy and great synod that, in some districts and cities, the deacons administer the Eucharist to the presbyters [i.e., priests], whereas neither canon nor custom permits that they who have no right to offer [the Eucharistic sacrifice] s hould give the Body of Christ to them that do offer [it] " (Canon 18 [A.D. 325]).
The flesh is anointed, so that the soul may be dedicated to holiness. The flesh is signed, so that the soul too may be fortified. The flesh is shaded by the imposition of hands, so that the soul too may be illuminated by the Spirit. The flesh feeds on the Body and Blood of Christ, so that the soul too may fatten on God. (Tertullian)
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 to our bodies. When, therefore, the mixed cup and the baked bread receives the Word of God and becomes the Eucharist, the Body of Christ , and from these the substance of our body is increased and supported, how can they say that the flesh is not capable of receiving the gift of God, which is eternal life. (Ireaneus of Lyons)
c. 150 AD
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 nourished, is both the flesh and blood of that incarnate Jesus. (St Justin Martyr)
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 . (Ignatius of Antioch)
They [the Gnostics] 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 the Father, in his goodness, raised up again. (Ignatius of Antioch)
Now consider this, Ignatius learned from the Apostles themselves. Did he misunderstand them? Isn’t it much more likely that he remembered what he was taught and taught others who would succeed him as Justin Martyr did, and Irenaeus, Augustine even councils speaking for the whole church teaching as the first followers of the original Apostles taught and all speaking with one voice on the matter?