First of all, realize the all Christians believed that the bread and wine truly becomes the body and blood of Christ up to the sixteenth century. That’s a long time. The largest and oldest Christian Church still does—as well as the various Orthodox churches. So we don’t take this matter lightly. There has to be something credible about it.
It is true that for the Jews, consuming blood was an abomination. Scripture does tell us that many of the disciples of Jesus could not accept this and from that point on did not follow Him (Jn 6:66), BUT not all of them. “Then Jesus said to the Twelve, ‘What about you, do you want to go away too?’ Simon Peter answered, ‘Lord, who shall we go to? You have the message of eternal life, and we believe; we know that you are the Holy One of God’” (Jn 6:67-69). THESE did accept what He said—not because they understood, but because they believed in Him.
If Jesus were merely speaking symbolically, He could easily have called the other disciples back and explained that He wasn’t speaking literally. This He did not do.
Jesus, we believe, is God. That God would love His creatures so much that He would actually become one of them, and then allow them to torture Him and put Him to death for their benefit is something that boggles the mind. The Jews could not conceive that God would do such a thing. And yet this divine self-gift gives us a window into what comprises His infinite love. This is the only experience we have of anything that has no limit. Everything else we know is finite; limited. The moment in which He died is an eternal moment. It covers every person who lived on this earth before Good Friday and everyone who was to live after it. It TRANCENDS time.
The Church and everything about it is incarnational because Jesus became incarnate. He used water and spittle and bread and wine and His very body and blood to minister to those who needed Him. Since Jesus is God, if He said that the bread and wine actually becomes His body and blood, then those who acknowledge His divinity, should have no difficulty in believing this to be true because, like the Twelve, they believe in Him. It is certainly no more extraordinary than His incarnation!
Since the moment of His death transcends time, to celebrate it in time is not to create another passion and death; it is to worship Him in that very passion here and now in the concrete manner of His devising.
See:
catholic.com/library/Real_Presence.asp
catholic.com/library/Sacrifice_of_the_Mass.asp
Fr. Vincent Serpa, O.P.