Catholics and Protestants have different views on the Eucharist or the Lord’s Supper as it is known in many Protestant faith traditions. Protestants and some Catholics have a hard time with Jesus’ command that we must eat His flesh and drink His blood.
To understand the Eucharist, you first have to know how the Jews thought about the Bread from Heaven. After receiving the miraculous bread from Heaven called Manna in the wilderness, the Jews kept some in the Ark of the Covenant with the 10 Commandments. Later when they built the portable Temple, specified by God to Moses, they had a special Altar for the Bread of the Presence and a pitcher of wine. This Altar was also present in the Temple built by Solomon and rebuilt by Herod. On the Day of Atonement (Yom Kippur), the Priests would take the Bread of the Presence out and show it to the faithful Jews while the Priests proclaimed ‘Behold God’s Love for You”. It was not a great leap for the Jews to believe that God could be present in the bread.
When Jesus said, in the Gospel of John chapter 6, "You have to eat My flesh and drink My blood" to have Eternal Life, all the Jews and the Disciples were scandalized by this saying. Everybody took Jesus seriously and left except for the 12 Disciples, and Judas decided then to betray Jesus because he didn't believe. It wasn't until the Last Supper that Disciples understood how they were to eat His flesh and drink His blood. This is covered in Matthew Chapter 26, Mark Chapter 14 and Luke Chapter 22. In each of these Gospels, Jesus says THIS IS My body about the bread, and THIS IS My blood about the cup of wine. The words are plain and easy to understand here. In First Corinthians chapter 10, Paul says the bread is a participation in the body of Christ and cup is a participation in the Blood of Christ. No symbolic language here either. Paul goes on to say in chapter 11 that we have no other practice and neither do the Churches of God. In the earliest rule of Faith for Christians, called the Didache, it says the Eucharist is only for the Baptized believer because we don't give that which is Holy to the dogs (unbaptized non-believers). In 107AD Ignatius of Antioch says the Eucharist is the medicine of immortality because Jesus said if you eat My flesh and drink My blood you will have eternal life. Ignatius also says to have nothing to do with the heretics that don't believe the Eucharist is the flesh and blood of our Lord. In 150AD Justin the Martyr says the bread and wine are prayed over and become the flesh and blood of our Savior Jesus Christ, and the Deacons take it to those who cannot attend. This shows Jesus is physically present in the bread and wine because it can be transported. Jesus is not just present symbolically or spiritually only during the Mass. His presence exists as long as it still looks like bread and wine. In 180AD Irenaeus explains the Eucharist has 2 realities: earthly and Heavenly.
The Catechism of the Catholic Church discusses the Eucharist in parts 1322 through 1419 because it is so central to our Faith. All of the Christian Churches that trace their founding to an Apostle believe in the presence of Jesus in the Eucharist. This is the original Christian understanding available only in the Catholic and Orthodox Churches.
It wasn’t until the 1500s that Martin Luther taught that Jesus was present under and around the bread and wine. John Calvin taught that Jesus was present spiritually during the Lords Supper only. It was Ulrich Zwingli that first proposed that the presence of Jesus was "only symbolic".