First of all, up to the 16th century virtually all Christians believed that the bread and wine truly becomes the body and blood of Christ. That’s a long time. The largest and oldest Christian Church still does—as do the Orthodox churches. So there has to be something credible about it.
It is true that for the Jews, consuming blood was an abomination. Scripture tells 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, to whom shall we go? 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 disciples 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. He did not. Jesus, we believe, is God. It boggles the mind that God loves his creatures so much that he became one of them, and then allowed them to torture him and put him to death for their benefit. The moment in which he died covers every person who lived on this earth before Good Friday and everyone who was to live after it. It transcends time.
The Church and everything about it is incarnational because Jesus became incarnate. He used water and spittle and bread and wine and his own body and blood to minister to those who needed him. Since Jesus is God, if he said that the bread and wine becomes his body and blood, then those who acknowledge his divinity should have no difficulty believing it 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: www.catholic.com/library/Sacrifice_of_the_Mass.asp.