"And this food is called among us Εὐχαριστία [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, 100AD-165AD, First Apology in defense of the Christians
you have to love this quote from Justin, he shows the Church taught baptismal regeneration and the Eucharist as the Body of Christ mid-2nd century, while many people who were personally taught by the Apostle John were still alive.
he contended for the Faith once delivered to the saints against unbelievers in his day, just as we deal with these unbelievers in our day.
nothing new under the sun.