Transubstantiation is a doctrine of the Roman Catholic Church. The Catechism of the Catholic Church defines this doctrine in section 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.’"
In other words, the Roman Catholic Church teaches that once an ordained priest blesses the bread of the Lord's Supper, it is transformed into the actual flesh of Christ (though it retains the appearance, odor, and taste of bread); and when he blesses the wine, it is transformed into the actual blood of Christ (though it retains the appearance, odor, and taste of wine). Is such a concept biblical? There are some Scriptures that, if interpreted strictly literally, would lead to the “real presence” of Christ in the bread and wine. Examples are John 6:32-58; Matthew 26:26; Luke 22:17-23; and 1 Corinthians 11:24-25. The passage pointed to most frequently is John 6:32-58 and especially verses 53-57, “Jesus said to them, ‘I tell you the truth, unless you eat the flesh of the Son of Man and drink His blood, you have no life in you. Whoever eats my flesh and drinks my blood has eternal life … For my flesh is real food and my blood is real drink. Whoever eats my flesh and drinks my blood remains in me, and I in him … so the one who feeds on me will live because of me.’”
Roman Catholics interpret this passage literally and apply its message to the Lord’s Supper, which they title the “Eucharist” or “Mass.” Those who reject the idea of transubstantiation interpret Jesus’ words in John 6:53-57 figuratively or symbolically. How can we know which interpretation is correct? Thankfully, Jesus made it exceedingly obvious what He meant. John 6:63 declares, “The Spirit gives life; the flesh counts for nothing. The words I have spoken to you are spirit and they are life.” Jesus specifically stated that His words are “spirit.” Jesus was using physical concepts, eating and drinking, to teach spiritual truth. Just as consuming physical food and drink sustains our physical bodies, so are our spiritual lives saved and built up by spiritually receiving Him, by grace through faith. Eating Jesus’ flesh and drinking His blood are symbols of fully and completely receiving Him in our lives.
The Scriptures declare that the Lord's Supper is a memorial to the body and blood of Christ (Luke 22:19; 1 Corinthians 11:24-25), not the actual consumption of His physical body and blood. When Jesus was speaking in John chapter 6, Jesus had not yet had the Last Supper with His disciples, in which He instituted the Lord’s Supper. To read the Lord’s Supper / Christian Communion back into John chapter 6 is unwarranted. For a more complete discussion of these issues, please read our article on the Holy Eucharist.
The most serious reason transubstantiation should be rejected is that it is viewed by the Roman Catholic Church as a "re-sacrifice" of Jesus Christ for our sins, or as a “re-offering / re-presentation” of His sacrifice. This is directly in contradiction to what Scripture says, that Jesus died "once for all" and does not need to be sacrificed again (Hebrews 10:10; 1 Peter 3:18). Hebrews 7:27 declares, "Unlike the other high priests, He (Jesus) does not need to offer sacrifices day after day, first for his own sins, and then for the sins of the people. He sacrificed for their sins ONCE for all when He offered Himself."