One of the bigger errors of the Catholic Church is the doctrine of Transubstantiation. Transubstantiation is the belief that when Jesus said the bread is His body, and the wine is His blood, He was speaking literally.
The problem with this theory is that Jesus said a lot of other things that are clearly not literal. I am the true vine (John 15:1). I am the door (John 10:9). You must be born again (John 3:3, 7). These things, and many more, are clearly not literal, and not even the Catholic Church claims they are (although I have experienced some trying to argue that Jesus is quite literally a door because shepherds would lie between the gaps in a wall like a door). So why is "this is my body and blood" considered to be the one time Jesus was speaking literally?
One fact that is all too often overlooked is that the earliest Church was primarily Jewish. There were a few gentiles, of course, but Christianity is an inherently Jewish faith, with a lot of the New Testament even being aimed directly at Jews. Now, fun fact: Jews do not consume blood. It is considered unclean to them (Leviticus 3:17; 17:10-11). And this transcends Mosaic law, too. Noah wasn't allowed to consume blood either (Genesis 9:4), despite being permitted to eat "everything" as the green plants.
And we know that, at the very least, Peter (supposedly the first Pope, so his view should really count in the Catholic worldview) was devout enough to obey this. In Acts 10:9-16, Peter is given a vision wherein God gives him a whole load of "unclean" animals and commands him to eat them. Peter's response? "Not so, Lord! For I have never eaten anything common or unclean." Never? But blood is unclean! So how could Peter possibly have said this if he believed he had consumed the blood of Christ? And why would he have even taken the cup without resistance if he thought he was consuming literal blood? It should have taken at least 4 commands from Christ, as not even 3 commands from God could convince Him to eat a pork chop.
And there's more. Peter was present at the Council of Jerusalem in Acts 15. The final ruling? Abstain from blood (Acts 15:20, 29). Note that "except the Eucharist" is conspicuously absent here. In fact, nowhere in the Bible is there any kind of clarification that there is literally a transformation of the bread and wine. Certainly not that this transformation occurs when consecrated by a priest, especially since the Bible says all believers are priests (1 Peter 2:9). Every reference to the bread and wine is in a symbolic nature, not a literal one, but so that we may proclaim the Lord's death until He comes (1 Corinthians 11:26). It is an act of remembrance (Luke 22:19), not a reception of grace!
Transubstantiation is completely alien to the Bible, and yet it is a part of one of Catholicism's 7 sacraments. The Catholic Church is filled to the brim with obvious lies like this, and anyone with a Bible can prove it. Far better to trust Christ, whose blood was shed for us, than Rome, who are so opposed to Christ that they actively suppressed His word until they could suppress no more.