If the early church fathers, including Martin Luther and John Calvin, believed in the real presence of Christ in the Eucharist (communion) also known as Transubstantiation and this is supported by John 6 and 1 Corinthians 10:16; 11:27-31, then why do most modern day Protestants reject such a biblical idea?
Transubstantiation is defined as: “The teaching that during the Mass, at the consecration in the Lord’s Supper (Communion), the elements of the Eucharist, bread and wine, are transformed into the actual body and blood of Jesus and that they are no longer bread and wine but only retain their appearance of bread and wine.” This teaches that when one partakes in the Mass (Catholics) or Communion (non-Catholics), the bread and wine literally turn into the body and blood of Christ.
The ‘early church fathers’ were considered to be those who lived and taught within two generations of the Apostles. Men such as Clement of Rome, Polycarp of Smyrna, Tertullian, Jerome, etc. along with others, were considered the early church fathers. That era of men ended around 700 AD. Martin Luther was born in 1483. John Calvin was born in 1509. We cannot think of these men as early church fathers.
As many already know, Martin Luther was very instrumental in the Protestant movement. He broke away from the Roman Catholic Church and changed many of his doctrinal views, rejecting the transubstantiation view. He eventually adopted what is called the ‘sacramental union’ which teaches that during communion, “the consecrated bread is united with the body of Christ and the consecrated wine is united with the blood of Christ by virtue of Christ’s original institution with the result that anyone eating and drinking these “elements”—the consecrated bread and wine—really eats and drinks the physical body and blood of Christ as well.” He wrote about this in his work: CONFESSION CONCERNING CHRIST’S SUPPER in 1528. Although we do not agree with Luther’s teachings on this, we clearly see that he rejected the thought of transubstantiation.
John Calvin, who was born a little later than Martin Luther, also rejected the teaching of transubstantiation. He wrote in his book THE BABYLONIAN CAPTIVITY OF THE CHURCH (1520) that “the sacraments are signs.” He recognized that the words of the Lord Jesus in stating “This is my body” and “This is my blood” (Matthew 26:26, 28) while instituting the Remembrance Feast was using these elements as SYMBOLS or TYPES of His body and blood. So, we see that two points mentioned in your question were incorrect. Luther and Calvin were not part of the ‘early church fathers’, and they both rejected the thought of transubstantiation.
You mentioned John, chapter 6 as proof of transubstantiation. Let’s consider a couple of verses from that wonderful chapter. The Lord said in verse 51, “I am the living bread which came down from heaven: if any man eat of this bread, he shall live for ever: and the bread that I will give is my flesh, which I will give for the life of the world.” He went on to say in verses 53-55, “Verily, verily, I say unto you, Except ye eat the flesh of the Son of man, and drink his blood, ye have no life in you. Whoso eateth my flesh, and drinketh my blood, hath eternal life; and I will raise him up at the last day. For my flesh is meat indeed, and my blood is drink indeed.” As we have stated before in Answers From the Book, we believe that all scripture should be taken as literal unless it is obvious that it cannot be. This is such a case. Is Christ a loaf of bread? Would the Lord have us take part in an act of cannibalism? Surely not! It is obvious to the careful reader that the Lord is speaking of ‘appropriating’ (taking hold of or receiving) to ourselves Christ as our savior. Certainly John 6:53-55 is not speaking of the act of Communion. Here, the Lord says that if one does not eat of His body and drink of His blood, he has no life! Communion is for those who already possess eternal life in Christ. The Lord is definitely speaking of receiving Him as savior in order to have life. “He that hath the Son hath life.” (1 John 5:12) (273.10)